Merck & Co., Inc. (Form: 8-K, Received: 09/09/2025 16:33:40)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 OR 15(d) of

the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported) September 9, 2025

Merck & Co., Inc.

(Exact name of registrant as specified in its charter)


New Jersey	1-6571	22-1918501
(State or other jurisdiction	(Commission	(I.R.S Employer
of incorporation)	File Number)	Identification No.)


126 East Lincoln Avenue, Rahway, New Jersey			07065
(Address of principal executive offices)			(Zip Code)

(Registrant’s telephone number, including area code) (908) 740-4000

Not Applicable

(Former name or former address, if changed since last report.)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class

Trading Symbol(s)

Name of each exchange on which registered

Common Stock ($0.50 par value)

MRK

New York Stock Exchange

1.875% Notes due 2026

MRK/26

New York Stock Exchange

3.250% Notes due 2032

MRK/32

New York Stock Exchange

2.500% Notes due 2034

MRK/34

New York Stock Exchange

1.375% Notes due 2036

MRK 36A

New York Stock Exchange

3.500% Notes due 2037

MRK/37

New York Stock Exchange

3.700% Notes due 2044

MRK/44

New York Stock Exchange

3.750% Notes due 2054

MRK/54

New York Stock Exchange

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 8.01 Other Events.

On September 9, 2025, Merck & Co., Inc. (the “Company”) closed an underwritten public offering of $500,000,000 aggregate principal amount of Floating Rate Notes due 2027 (the “Floating Rate Notes”), $750,000,000 aggregate principal amount of 3.850% Notes due 2027 (the “2027 Notes”), $750,000,000 aggregate principal amount of 4.150% Notes due 2030 (the “2030 Notes”), $1,000,000,000 aggregate principal amount of 4.550% Notes due 2032 (the “2032 Notes”), $1,750,000,000 aggregate principal amount of 4.950% Notes due 2035 (the “2035 Notes”) and $1,250,000,000 aggregate principal amount of 5.700% Notes due 2055 (the “2055 Notes” and, together with the Floating Rate Notes, the 2027 Notes, the 2030 Notes, the 2032 Notes and the 2035 Notes, collectively, the “Notes”) under the Company’s Registration Statement on Form S-3ASR (Registration No. 333-278066), originally filed with the Securities and Exchange Commission (the “Commission”) on March 19, 2024, as amended by Post-Effective Amendment No. 1, filed with the Commission on May 14, 2024.

The Notes are being issued under an indenture dated as of January 6, 2010, between the Company and U.S. Bank Trust National Association, as trustee, a copy of which was attached as Exhibit 4.1 to the Company’s Current Report on Form 8-K previously filed with the Securities and Exchange Commission on December 10, 2010 and is incorporated herein by reference. Copies of the officers’ certificate for each series of the Notes (including forms of each of the respective Notes attached thereto) pursuant to Section 301 of the indenture governing the Notes are attached hereto as Exhibits 4.1, 4.2, 4.3, 4.4, 4.5 and 4.6 and are incorporated herein by reference. The legal opinion related to these Notes is attached hereto as Exhibit 5.1 and is incorporated herein by reference.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits


Exhibit 4.1						Floating Rate Notes due 2027 Officers’ Certificate of the Company dated September 9, 2025, including form of the Floating Rate Notes.
Exhibit 4.2						3.850% Notes due 2027 Officers’ Certificate of the Company dated September 9, 2025, including form of the 2027 Notes.
Exhibit 4.3						4.150% Notes due 2030 Officers’ Certificate of the Company dated September 9, 2025, including form of the 2030 Notes.
Exhibit 4.4						4.550% Notes due 2032 Officers’ Certificate of the Company dated September 9, 2025, including form of the 2032 Notes.
Exhibit 4.5						4.950% Notes due 2035 Officers’ Certificate of the Company dated September 9, 2025, including form of the 2035 Notes.
Exhibit 4.6						5.700% Notes due 2055 Officers’ Certificate of the Company dated September 9, 2025, including form of the 2055 Notes.
Exhibit 5.1						Opinion and Consent of Jennifer Zachary, Esq., Executive Vice President and General Counsel of the Company.
Exhibit 23.1						Consent of Jennifer Zachary, Esq., Executive Vice President and General Counsel of the Company (contained in Exhibit 5.1 to this Current Report on Form 8-K).
Exhibit 104						Cover Page Interactive Data File (embedded within the Inline XBRL document).

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.


	Merck & Co., Inc.

Date: September 9, 2025	By:	/s/ Kelly E. W. Grez
		Kelly E. W. Grez
		Corporate Secretary

Exhibit 4.1

FLOATING RATE NOTES DUE 2027

MERCK & CO., INC.

Officers’ Certificate

Pursuant to the unanimous written consent and resolutions (collectively, the “Resolutions”) of the Board of Directors of Merck & Co., Inc. (the “Company”) (i) duly adopted and dated March 14, 2024 and (ii) adopted at a meeting duly called and held on November 30, 2021 (at which meeting a quorum was present and acting throughout), which authorized the Company to issue and sell its debt securities and empowered an Authorized Officer (as defined in the Resolutions) to approve the form and terms of such debt securities, Melissa Leonard, Senior Vice President and Treasurer, and Kelly E.W. Grez, Corporate Secretary, each hereby approves and establishes under the Indenture, dated as of January 6, 2010 (the “Indenture”), between the Company and U.S. Bank Trust National Association, as Trustee (the “Trustee”), a series of debt securities the terms of which are as follows:

1. The title of the debt securities of such series shall be the Floating Rate Notes due 2027 (the “2027 Floating Rate Notes”).

2. The aggregate principal amount of the 2027 Floating Rate Notes which may be authenticated and delivered under the Indenture is initially limited to $500,000,000, except for 2027 Floating Rate Notes authenticated and delivered upon registration or transfer of, or in exchange for, or in lieu of, other 2027 Floating Rate Notes of the series pursuant to Section 304, 305, 306, 906 or 1107 of the Indenture and except for any 2027 Floating Rate Notes which, pursuant to Section 303 of the Indenture, are deemed never to have been authenticated and delivered under the Indenture.

3. The Company shall have the right from time to time, without the consent of the Holders of the 2027 Floating Rate Notes, to create and issue additional notes with the same terms and conditions as the 2027 Floating Rate Notes except for the issue date, issue price and the first payment of interest thereon (“Additional Notes”), provided that if the Additional Notes are not fungible with the previously outstanding 2027 Floating Rate Notes for U.S. federal income tax purposes, such Additional Notes will have a separate CUSIP. Additional Notes will

be consolidated with and will form a single series with the previously outstanding 2027 Floating Rate Notes. Any election by the Company to so increase such aggregate principal amount shall be evidenced by a certificate of an Authorized Officer or Authorized Officers. No Additional Notes may be issued if an Event of Default has occurred or is continuing with respect to the 2027 Floating Rate Notes.

4. The 2027 Floating Rate Notes shall be issued in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

5. The proceeds to the Company (after deducting the underwriting discounts and commissions but before deducting certain expenses payable by the Company in connection with the issuance of the 2027 Floating Rate Notes) shall be 99.850% of the aggregate principal amount of the 2027 Floating Rate Notes.

6. The maturity date on which the principal of each of the 2027 Floating Rate Notes is payable shall be September 15, 2027.

7. The 2027 Floating Rate Notes shall bear interest at a floating rate, reset quarterly on each Floating Rate Interest Payment Date (as defined below), equal to Compounded SOFR (as defined below), plus 0.460%. In no event will the interest on the 2027 Floating Rate Notes be less than zero. Interest on the 2027 Floating Rate Notes will be payable quarterly in arrears on March 15, June 15, September 15 and December 15 of each year, beginning December 15, 2025, and at maturity (each a “Floating Rate Interest Payment Date”). An interest period means the period from and including a Floating Rate Interest Payment Date (or, in the case of the initial interest period, from and including September 9, 2025) to, but excluding, the immediately succeeding Floating Rate Interest Payment Date (such succeeding Floating Rate Interest Payment Date, the “Latter Floating Rate Interest Payment Date”); provided that the final interest period for the 2027 Floating Rate Notes will be the period from and including the Floating Rate Interest Payment Date immediately preceding the maturity date of the 2027 Floating Rate Notes to, but excluding, the maturity date. The initial interest period is September 9, 2025 through December 15, 2025. The interest rate for the initial interest period will be Compounded SOFR determined on December 11, 2025, plus 0.460%. Thereafter, the interest rate for any interest period will be Compounded SOFR, as determined on the applicable date that is the second U.S. Government Securities Business Day (as defined below) preceding such Floating Rate Interest Payment Date (the “Interest Determination Date”), plus a margin of 0.460%.

8. All payments of interest on the 2027 Floating Rate Notes due on any Floating Rate Interest Payment Date will be made to the persons in whose names the 2027 Floating Rate Notes are registered at the close of business on the 15th calendar day immediately preceding the Floating

Rate Interest Payment Date (whether or not a business day). However, interest that the Company pays on the maturity date will be payable to the person to whom the principal will be payable. Interest on the 2027 Floating Rate Notes will be calculated on the basis of a 360-day year and the actual number of days in the Observation Period (as defined below).

9. Interest on the 2027 Floating Rate Notes will accrue from and including the most recent Floating Rate Interest Payment Date or, if there has not yet been a Floating Rate Interest Payment Date, from the settlement date of the 2027 Floating Rate Notes. If a Floating Rate Interest Payment Date, other than the maturity date, falls on a day that is not a business day, the interest payment will be postponed to the next day that is a business day, except that if that business day is in the next succeeding calendar month, the Floating Rate Interest Payment Date will be the immediately preceding business day. If the maturity date of the 2027 Floating Rate Notes falls on a day that is not a business day, the payment of interest and principal will be made on the next succeeding business day, and no interest on such payment will accrue for the period from and after the maturity date.

10. U.S. Bank Trust National Association, or its successor appointed by the Company, will act as calculation agent. The Company may change the calculation agent with respect to the 2027 Floating Rate Notes at any time without notice to the holders of the 2027 Floating Rate Notes. The interest rate and amount of interest to be paid on the 2027 Floating Rate Notes for each interest period will be determined by the calculation agent. All determinations made by the calculation agent, in the absence of manifest error, will be conclusive for all purposes and binding on the Company and the holders of the 2027 Floating Rate Notes.

11. The amount of interest accrued and payable on the 2027 Floating Rate Notes for each interest period will be equal to the product of (i) the outstanding principal amount of the 2027 Floating Rate Notes multiplied by (ii) the product of (a) the interest rate for the relevant interest period multiplied by (b) the quotient of the actual number of calendar days in such Observation Period divided by 360.

12. “Compounded SOFR” means, with respect to any interest period, the rate computed in accordance with the following formula set forth below (and the resulting percentage will be rounded, if necessary, to the nearest one hundred-thousandth of a percentage point (e.g., 9.753973% (or .09753973) being rounded down to 9.75397% (or .0975397) and 9.753978% (or .09753978) being rounded up to 9.75398% (or .0975398)):

where:

“SOFR IndexStart” is the SOFR Index value for the day that is two U.S. Government Securities Business Days preceding the first date of the relevant interest period;

“SOFR IndexEnd” is the SOFR Index value for the day that is two U.S. Government Securities Business Days preceding the Latter Floating Rate Interest Payment Date relating to such interest period (or in the final interest period, preceding the maturity date); and

“dc” is the actual number of calendar days from (and including) SOFR IndexStart to (but excluding) SOFR IndexEnd (the actual number of calendar days in the applicable Observation Period).

For purposes of determining Compounded SOFR, “SOFR Index” means, with respect to any U.S. Government Securities Business Day:

(1) the SOFR Index value as published by the New York Federal Reserve as such index appears on the New York Federal Reserve’s Website at 3:00 p.m. (New York time) on such U.S. Government Securities Business Day (the “SOFR Determination Time”); provided that:

(2) if a SOFR Index value does not so appear as specified in clause (1) above at the SOFR Determination Time, then:

(i) if a Benchmark Transition Event and its related Benchmark Replacement Date (each as defined below) have not occurred with respect to SOFR, then Compounded SOFR shall be the rate determined pursuant to the “SOFR Index Unavailable” provisions described below; or

(ii) if a Benchmark Transition Event and its related Benchmark Replacement Date have occurred with respect to SOFR, then Compounded SOFR shall be the rate determined pursuant to the “Effect of a Benchmark Transition Event” provisions described below.

“New York Federal Reserve” means the Federal Reserve Bank of New York (or a successor administrator of the Secured Overnight Financing Rate).

“New York Federal Reserve’s Website” means the website of the New York Federal Reserve, currently at http://www.newyorkfed.org, or any successor source.

“Observation Period” means, in respect of each interest period, the period from and including two U.S. Government Securities Business Days preceding the first date of such relevant interest period to but excluding two U.S. Government Securities Business Days preceding the Latter Floating Rate Interest Payment Date for such interest period (or in the final interest period, preceding the maturity date); provided that the first Observation Period shall be the period from and including two U.S. Government Securities Business Days preceding the settlement date of the 2027 Floating Rate Notes to, but excluding, the two U.S. Government Securities Business Days preceding the first Floating Rate Interest Payment Date.

“Secured Overnight Financing Rate” or “SOFR” means the daily secured overnight financing rate as provided by the New York Federal Reserve on the New York Federal Reserve’s Website.

“U.S. Government Securities Business Day” means any day except for a Saturday, Sunday or a day on which the Securities Industry and Financial Markets Association recommends that the fixed income departments of its members be closed for the entire day for purposes of trading in U.S. government securities.

Notwithstanding anything contained herein, the Indenture, the 2027 Floating Rate Notes or in any other documentation relating to the 2027 Floating Rate Notes, if the Company or its designee determine on or prior to the relevant Reference Time (as defined below) that a Benchmark Transition Event and its related Benchmark Replacement Date have occurred with respect to determining Compounded SOFR, then the benchmark replacement provisions set forth below under “Effect of a Benchmark Transition Event” will thereafter apply to all determinations of the rate of interest payable on the 2027 Floating Rate Notes. For the avoidance of doubt, in accordance with the benchmark replacement provisions, after a Benchmark Transition Event and its related Benchmark Replacement Date have occurred, the interest rate for each interest period on the 2027 Floating Rate Notes will be an annual rate equal to the sum of the Benchmark Replacement (as defined below) and the applicable margin (not to be less than zero).

13. If a SOFR IndexStart or SOFR IndexEnd is not published on the associated Interest Determination Date and a Benchmark Transition Event and its related Benchmark Replacement Date have not occurred with respect to the Secured Overnight Financing Rate, “Compounded SOFR” means, for the applicable interest period for which such index is not available, the rate of return on a daily compounded interest investment calculated in accordance with the formula for SOFR Averages, and definitions required for such formula, published on the New York Federal Reserve’s Website at https://www.newyorkfed.org/markets/treasury-repo-reference-rates-information. For the purposes of this provision, references in the SOFR

Averages compounding formula and related definitions to “calculation period” shall be replaced with “Observation Period” and the words “that is, 30-, 90-, or 180- calendar days” shall be removed. If the daily Secured Overnight Financing Rate (“SOFRi”) does not so appear for any day, “i” in the Observation Period, SOFRi for such day “i” shall be SOFR published in respect of the first preceding U.S. Government Securities Business Day for which the Secured Overnight Financing Rate was published on the New York Federal Reserve’s Website.

14. If the Company or its designees determine on or prior to the relevant Reference Time that a Benchmark Transition Event and its related Benchmark Replacement Date have occurred with respect to the then-current Benchmark, the Benchmark Replacement will replace the then-current Benchmark for all purposes relating to the 2027 Floating Rate Notes in respect of all determinations on such date and for all determinations on all subsequent dates.

In connection with the implementation of a Benchmark Replacement, the Company or its designee will have the right to make Benchmark Replacement Conforming Changes from time to time.

Any determination, decision or election that may be made by the Company or its designee pursuant to this Section 14, including a determination with respect to a tenor, rate or adjustment or of the occurrence or non-occurrence of an event, circumstance or date and any decision to take or refrain from taking any action or any selection:

(1) will be conclusive and binding absent manifest error;

(2) if made by the Company, will be made in its sole discretion;

(3) if made by the Company’s designee, will be made after consultation with the Company, and such designee will not make any such determination, decision or election to which the Company objects; and

(4) notwithstanding anything to the contrary herein, the 2027 Floating Rate Notes or in the other documentation relating to the 2027 Floating Rate Notes, including the Indenture, shall become effective without consent from the holders of the 2027 Floating Rate Notes or any other party.

As used herein, the following terms have the meanings assigned to them:

“Benchmark” means, initially, Compounded SOFR, as such term is defined above; provided that if the Company or its designee determines on or prior to the Reference Time that a Benchmark Transition Event and its related Benchmark Replacement Date have occurred with respect to Compounded SOFR (or the published daily SOFR Index used in the calculation thereof) or the then-current Benchmark, then “Benchmark” means the applicable Benchmark Replacement.

“Benchmark Replacement” means the first alternative set forth in the order below that can be determined by the Company or its designee as of the Benchmark Replacement Date:

(1) the sum of (a) the alternate rate of interest that has been selected or recommended by the Relevant Governmental Body as the replacement for the then-current Benchmark and (b) the Benchmark Replacement Adjustment;

(2) the sum of (a) the ISDA Fallback Rate and (b) the Benchmark Replacement Adjustment; or

(3) the sum of (a) the alternate rate of interest that has been selected by the Company or its designee as the replacement for the then-current Benchmark giving due consideration to any industry-accepted rate of interest as a replacement for the then-current Benchmark for U.S. dollar-denominated floating rate notes at such time and (b) the Benchmark Replacement Adjustment

“Benchmark Replacement Adjustment” means the first alternative set forth in the order below that can be determined by the Company or its designee as of the Benchmark Replacement Date:

(1) the spread adjustment, or method for calculating or determining such spread adjustment (which may be a positive or negative value or zero), that has been selected or recommended by the Relevant Governmental Body for the applicable Unadjusted Benchmark Replacement;

(2) if the applicable Unadjusted Benchmark Replacement is equivalent to the ISDA Fallback Rate, the ISDA Fallback Adjustment; or

(3) the spread adjustment (which may be a positive or negative value or zero) that has been selected by the Company or its designee giving due consideration to any industry-accepted spread adjustment, or method for calculating or determining such spread adjustment, for the replacement of the then-current Benchmark with the applicable Unadjusted Benchmark Replacement for U.S. dollar-denominated floating rate notes at such time.

The Benchmark Replacement Adjustment shall not include the margin specified herein, and such margin shall be applied to the Benchmark Replacement to determine the interest payable on the 2027 Floating Rate Notes.

“Benchmark Replacement Conforming Changes” means, with respect to any Benchmark Replacement, any technical, administrative or operational changes (including changes to the definition of the interest period, timing and frequency of determining rates and making payments of interest, rounding of amounts or tenors and other technical, administrative or operational matters) that the Company or its designee decides may be appropriate to reflect the adoption of such Benchmark Replacement in a manner substantially consistent with market practice (or, if the Company or its designee decides that adoption of any portion of such market practice is not administratively feasible or if the Company or its determines that no market practice for use of the Benchmark Replacement exists, in such other manner as the Company or its designee determines is reasonably practicable).

“Benchmark Replacement Date” means the earliest to occur of the following events with respect to the then-current Benchmark (including any daily published component used in the calculation thereof):

(1) in the case of clause (1) or (2) of the definition of “Benchmark Transition Event,” the later of (a) the date of the public statement or publication of information referenced therein and (b) the date on which the administrator of the Benchmark permanently or indefinitely ceases to provide the Benchmark (or such component); or

(2) in the case of clause (3) of the definition of “Benchmark Transition Event,” the date of the public statement or publication of information referenced therein.

For the avoidance of doubt, if the event that gives rise to the Benchmark Replacement Date occurs on the same day as, but earlier than, the Reference Time in respect of any determination, the Benchmark Replacement Date will be deemed to have occurred prior to the Reference Time for such determination.

For the avoidance of doubt, for purposes of the definitions of Benchmark Replacement Date and Benchmark Transition Event, references to Benchmark also include any reference rate underlying such Benchmark.

“Benchmark Transition Event” means the occurrence of one or more of the following events with respect to the then-current Benchmark (including any daily published component used in the calculation thereof):

(1) a public statement or publication of information by or on behalf of the administrator of the Benchmark (or such component) announcing that such administrator has ceased or will cease to provide the Benchmark (or such component), permanently or indefinitely; provided that, at the time of such statement or publication, there is no successor administrator that will continue to provide the Benchmark (or such component);

(2) a public statement or publication of information by the regulatory supervisor for the administrator of the Benchmark (or such component), the central bank for the currency of the Benchmark (or such component), an insolvency official with jurisdiction over the administrator for the Benchmark (or such component), a resolution authority with jurisdiction over the administrator for the Benchmark (or such component) or a court or an entity with similar insolvency or resolution authority over the administrator for the Benchmark (or such component), which states that the administrator of the Benchmark (or such component) has ceased or will cease to provide the Benchmark (or such component) permanently or indefinitely; provided that, at the time of such statement or publication, there is no successor administrator that will continue to provide the Benchmark (or such component); or

(3) a public statement or publication of information by the regulatory supervisor for the administrator of the Benchmark announcing that the Benchmark is no longer representative.

“ISDA Definitions” means the 2006 ISDA Definitions published by the International Swaps and Derivatives Association, Inc. or any successor thereto, as amended or supplemented from time to time, or any successor definitional booklet for interest rate derivatives published from time to time.

“ISDA Fallback Adjustment” means the spread adjustment (which may be a positive or negative value or zero) that would apply for derivatives transactions referencing the ISDA Definitions to be determined upon the occurrence of an index cessation event with respect to the Benchmark.

“ISDA Fallback Rate” means the rate that would apply for derivatives transactions referencing the ISDA Definitions to be effective upon the occurrence of an index cessation date with respect to the Benchmark for the applicable tenor excluding the applicable ISDA Fallback Adjustment.

“Reference Time” with respect to any determination of the Benchmark means (1) if the Benchmark is Compounded SOFR, the SOFR Determination Time, and (2) if the Benchmark is not Compounded SOFR, the time determined by the Company or its designee after giving effect to the Benchmark Replacement Conforming Changes.

“Relevant Governmental Body” means the Federal Reserve Board and/or the New York Federal Reserve, or a committee officially endorsed or convened by the Federal Reserve Board and/or the New York Federal Reserve or any successor thereto.

“Unadjusted Benchmark Replacement” means the Benchmark Replacement excluding the Benchmark Replacement Adjustment.

None of the trustee, the paying agent or the calculation agent shall be under any obligation (i) to monitor, determine or verify the unavailability or cessation of SOFR or the SOFR Index or any other Benchmark, or whether or when there has occurred, or to give notice to any other transaction party of the occurrence of, any Benchmark Transition Event or related Benchmark Replacement Date, (ii) to select, determine or designate any Benchmark Replacement, or other successor or replacement benchmark index, or whether any conditions to the designation of such a rate or index have been satisfied, (iii) to select, determine or designate any Benchmark Replacement Adjustment, or other modifier to any replacement or successor index, or (iv) to determine whether or what Benchmark Replacement Conforming Changes are necessary or advisable, if any, in connection with any of the foregoing. In connection with the foregoing, each of the trustee, the paying agent and the calculation agent shall be entitled to conclusively rely on any determinations made by the Company or its designee without independent investigation, and none will have any liability for actions taken at the Company’s direction in connection therewith.

None of the trustee, the paying agent or the calculation agent shall be liable for any inability, failure or delay on its part to perform any of its duties set forth in the Indenture of the 2027 Floating Rate Notes as a result of the unavailability of SOFR, the SOFR Index or other applicable Benchmark Replacement, including as a result of any failure, inability, delay, error or inaccuracy on the part of any other transaction party in providing any direction, instruction, notice or information required or contemplated by the terms of the Indenture or the 2027 Floating Rate Notes and reasonably required for the performance of such duties. In connection with any determination made hereunder, none of the trustee, the paying agent or the calculation agent shall be responsible or liable for the Company’s actions or omissions or for those of its designee, or

for any failure or delay in the performance by the Company or its designee, nor shall any of the trustee, the paying agent or the calculation agent be under any obligation to oversee or monitor the Company’s performance or that of its designee.

15. The 2027 Floating Rate Notes will not be redeemable prior to maturity.

16. Payment of the principal and interest on the 2027 Floating Rate Notes will be made at the office or agency of the Company maintained for that purpose in New York, New York (initially, the Corporate Trust Office of the Trustee), provided that at the option of the Company payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Security Register.

17. The provisions on defeasance and covenant defeasance in Article Thirteen of the Indenture shall apply to the 2027 Floating Rate Notes.

18. The 2027 Floating Rate Notes shall be issued in the form of one or more Book-Entry Securities and the Depository for such Book-Entry Securities shall be The Depository Trust Company, Clearstream Banking societé anonyme and Euroclear Bank SA/NV.

19. The form of the 2027 Floating Rate Notes attached hereto as Annex A is hereby approved.

Capitalized terms used herein and not otherwise defined herein have the meanings specified in the Indenture.

IN WITNESS WHEREOF, we have hereunto signed our names this ninth day of September, 2025.


			/s/ Melissa Leonard
			Name:			Melissa Leonard
			Title:			Senior Vice President and Treasurer


			/s/ Kelly E. W. Grez
			Name:			Kelly E. W. Grez
			Title:			Corporate Secretary

[Section 301 Officers’ Certificate – 2027 Floating Rate Notes]

Annex A

[FORM OF GLOBAL NOTES]


REGISTERED			REGISTERED
No. R-[1]			PRINCIPAL AMOUNT: $[●]1
CUSIP NO. 58933Y BU8

MERCK & CO., INC.

FLOATING RATE NOTES DUE 2027

This Security is a Book-Entry Security within the meaning of the Indenture referred to on the reverse hereof and is registered in the name of a Depository or a nominee of a Depository. This Security is exchangeable for Securities registered in the name of a Person other than the Depository or its nominee only in the limited circumstances described in the Indenture and this Security may not be transferred except as a whole by the Depository to a nominee of the Depository or by a nominee of the Depository to the Depository or another nominee of the Depository.

Unless this Certificate is presented by an authorized representative of The Depository Trust Company, a New York corporation (“DTC”), to the Company or its agent for registration of transfer, exchange or payment, and any Certificate issued is registered in the name of Cede & Co. or in such other name as is requested by an authorized representative of DTC (and any payment hereon is made to Cede & Co. or to such other entity as is requested by an authorized representative of DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL inasmuch as the registered owner hereof, Cede & Co., has an interest herein.

1 On September 9, 2025, the 2027 Floating Rate Notes will be issued in the form of one Book-Entry Security in the principal amount of $500,000,000.

A-2

Merck & Co., Inc., a New Jersey corporation (hereinafter called the “Company”, which term includes any successor corporation under the Indenture hereinafter referred to), for value received, hereby promises to pay to Cede & Co., as nominee for The Depository Trust Company, or registered assigns, the principal sum of [●] Hundred Million Dollars ($[●]) on September 15, 2027, and to pay interest thereon from and including September 9, 2025 or from the most recent Floating Rate Interest Payment Date to which interest has been paid or duly provided for, quarterly in arrears on March 15, June 15, September 15 and December 15 in each year and at Maturity, commencing on December 15, 2025, at a floating rate until the principal hereof is paid or made available for payment, and (to the extent that the payment of such interest shall be legally enforceable) at the interest rate specified above on any overdue principal and premium and on any overdue installment of interest. The interest so payable, and punctually paid or duly provided for, on any Floating Rate Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be the 15th calendar day (whether or not a Business Day in New York City) immediately preceding such Floating Rate Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Securities of this series may be listed, and upon such notice as may be required by such exchange, all as more fully provided in said Indenture.

The Company will at all times appoint and maintain a Paying Agent (which may be the Trustee) authorized by the Company to pay the principal of (and premium, if any) or interest on any Securities of this series on behalf of the Company and having an office or agency (the “Paying Agent Office”) in The City of New York, where Securities of this series may be presented or surrendered for payment and where notices, designations or requests in respect of payments with respect to Securities of this series may be served. The Company has initially appointed U.S. Bank Trust National Association as such Paying Agent, with the Paying Agent Office currently at 100 Wall Street, New York, New York 10005. The Company will give prompt written notice to the Trustee of any change in such appointment.

Payment of the principal of (and premium, if any) and interest on this Security will be made in immediately available funds upon surrender of such Security at the Corporate Trust Office of U.S. Bank Trust National Association, in the Borough of Manhattan, The City of New York in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts. Payments of interest on any Security of this series (other than at the Maturity of such Security) will be made by check mailed to the address of the Person entitled thereto as it appears in the Security Register or by wire transfer to such account as may have been appropriately designated in writing no later than the relevant Regular Record Date to the Paying Agent by such Person.

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Reference is hereby made to the further provisions of this Security set forth on the reverse hereof, which further provisions shall for all purposes have the same effect as if set forth at this place.

Unless the certificate of authentication hereon has been executed by the Trustee referred to on the reverse hereof by manual signature, this Security shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

[Signature page follows]

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IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed under its corporate seal.

Dated: September 9, 2025

MERCK & CO., INC.

By:

Name:

Title:

Attest:

By: _____________________

Name:

Title:

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CERTIFICATE OF AUTHENTICATION

This is one of the Securities of the series designated herein referred to in the within-mentioned Indenture.


			U.S. BANK TRUST NATIONAL ASSOCIATION, As Trustee


			By:
						Authorized Officer

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[REVERSE OF SECURITY]

MERCK & CO., INC.

FLOATING RATE NOTES DUE 2027

This Security is one of a duly authorized issue of securities of the Company (herein called the “Securities”), issued and to be issued in one or more series under an Indenture, dated as of January 6, 2010, as amended and supplemented (herein called the “Indenture”), between the Company and U.S. Bank Trust National Association, as Trustee (herein called the “Trustee”, which term includes any successor trustee under the Indenture), to which Indenture and all indentures supplemental thereto reference is hereby made for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Company, the Trustee and the Holders of the Securities and of the terms upon which the Securities are, and are to be, authenticated and delivered.

The terms of the Securities include those stated in the Indenture and in the Officers’ Certificate dated September 9, 2025 (the “Officers’ Certificate”). This Security is subject to the terms in the Indenture and the Officers’ Certificate, and Holders are referred to the Indenture and the Officers’ Certificate for a statement of such terms. All terms used but not defined in this Security which are defined in the Indenture or in the Officers’ Certificate shall have the meanings assigned to them in the Indenture or Officers’ Certificate, as applicable.

This Security is one of the series designated on the face hereof. The aggregate principal amount of such series is $500,000,000 provided that the Company may increase such aggregate principal amount at any time.

The Company shall have the right from time to time, without the consent of the Holders of the Securities, to create and issue additional notes with the same terms and conditions as the Securities except for the issue date, issue price and the first payment of interest thereon (“Additional Notes”), provided that if the Additional Notes are not fungible with the previously outstanding Securities for U.S. federal income tax purposes, such Additional Notes will have a separate CUSIP. Additional Notes will be consolidated with and will form a single series with the previously outstanding Securities. Any election by the Company to so increase such aggregate principal amount shall be evidenced by a certificate of an Authorized Officer or Authorized Officers. No Additional Notes may be issued if an Event of Default has occurred or is continuing with respect to the Securities.

Payments of interest hereon with respect to any Floating Rate Interest Payment Date will include interest accrued to but excluding such Floating Rate Interest Payment Date.

This Security is not subject to any sinking fund.

The Securities will not be redeemable prior to the Stated Maturity.

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This Security shall bear interest at a floating rate, reset quarterly on each Floating Rate Interest Payment Date, equal to Compounded SOFR, plus 0.460%. In no event will the interest on the Securities be less than zero. Interest on the Securities will be payable quarterly in arrears on March 15, June 15, September 15 and December 15 of each year, beginning December 15, 2025, and at maturity (each a “Floating Rate Interest Payment Date”). An interest period means the period from and including a Floating Rate Interest Payment Date (or, in the case of the initial interest period, from and including September 9, 2025) to, but excluding, the immediately succeeding Floating Rate Interest Payment Date (such succeeding Floating Rate Interest Payment Date, the “Latter Floating Rate Interest Payment Date”); provided that the final interest period for the Securities will be the period from and including the Floating Rate Interest Payment Date immediately preceding the maturity date of the Securities to, but excluding, the maturity date. The initial interest period is September 9, 2025 through December 15, 2025. The interest rate for the initial interest period will be Compounded SOFR determined on December 11, 2025, plus 0.460%. Thereafter, the interest rate for any interest period will be Compounded SOFR, as determined on the applicable date that is the second U.S. Government Securities Business Day (as defined below) preceding such Floating Rate Interest Payment Date (the “Interest Determination Date”), plus a margin of 0.460%.

All payments of interest on the Securities due on any Floating Rate Interest Payment Date will be made to the persons in whose names the Securities are registered at the close of business on the 15th calendar day immediately preceding the Floating Rate Interest Payment Date (whether or not a business day) (each a “Regular Record Date”). However, interest that the Company pays on the maturity date will be payable to the person to whom the principal will be payable. Interest on the Securities will be calculated on the basis of a 360-day year and the actual number of days in the Observation Period.

Interest on the Securities will accrue from and including the most recent Floating Rate Interest Payment Date or, if there has not yet been a Floating Rate Interest Payment Date, from the settlement date of the floating rate notes. If a Floating Rate Interest Payment Date, other than the maturity date, falls on a day that is not a business day, the interest payment will be postponed to the next day that is a business day, except that if that business day is in the next succeeding calendar month, the Floating Rate Interest Payment Date will be the immediately preceding business day. If the maturity date of the Security falls on a day that is not a business day, the payment of interest and principal will be made on the next succeeding business day, and no interest on such payment will accrue for the period from and after the maturity date.

U.S. Bank Trust National Association, or its successor appointed by the Company, will act as calculation agent. The Company may change the calculation agent with respect to the Securities at any time without notice to the holders of the Securities. The interest rate and amount of interest to be paid on the Securities for each interest period will be determined by the calculation agent. All determinations made by the calculation agent, in the absence of manifest error, will be conclusive for all purposes and binding on the Company and the holders of the Securities.

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The amount of interest accrued and payable on the Securities for each interest period will be equal to the product of (i) the outstanding principal amount of the Securities multiplied by (ii) the product of (a) the interest rate for the relevant interest period multiplied by (b) the quotient of the actual number of calendar days in such Observation Period divided by 360.

As used herein the following terms have the meanings assigned to them

“Compounded SOFR” means, with respect to any interest period, the rate computed in accordance with the following formula set forth below (and the resulting percentage will be rounded, if necessary, to the nearest one hundred-thousandth of a percentage point (e.g., 9.753973% (or .09753973) being rounded down to 9.75397% (or .0975397) and 9.753978% (or .09753978) being rounded up to 9.75398% (or .0975398)):

where:

“SOFR IndexStart” is the SOFR Index value for the day that is two U.S. Government Securities Business Days preceding the first date of the relevant interest period;

“dc” is the actual number of calendar days from (and including) SOFR IndexStart to (but excluding) SOFR IndexEnd (the actual number of calendar days in the applicable Observation Period).

For purposes of determining Compounded SOFR, “SOFR Index” means, with respect to any U.S. Government Securities Business Day:

(2) if a SOFR Index value does not so appear as specified in clause (1) above at the SOFR Determination Time, then:

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“New York Federal Reserve” means the Federal Reserve Bank of New York (or a successor administrator of the Secured Overnight Financing Rate).

“New York Federal Reserve’s Website” means the website of the New York Federal Reserve, currently at http://www.newyorkfed.org, or any successor source.

“Observation Period” means, in respect of each interest period, the period from and including two U.S. Government Securities Business Days preceding the first date of such relevant interest period to but excluding two U.S. Government Securities Business Days preceding the Latter Floating Rate Interest Payment Date for such interest period (or in the final interest period, preceding the maturity date); provided that the first Observation Period shall be the period from and including two U.S. Government Securities Business Days preceding the settlement date of the floating rate notes to, but excluding, the two U.S. Government Securities Business Days preceding the first Floating Rate Interest Payment Date.

“Secured Overnight Financing Rate” or “SOFR” means the daily secured overnight financing rate as provided by the New York Federal Reserve on the New York Federal Reserve’s Website.

Notwithstanding anything contained herein, in the Indenture or in any other documentation relating to the Securities, if the Company or its designee determines on or prior to the relevant Reference Time (as defined below) that a Benchmark Transition Event and its related Benchmark Replacement Date have occurred with respect to determining Compounded SOFR, then the benchmark replacement provisions set forth below under “Effect of a Benchmark Transition Event” will thereafter apply to all determinations of the rate of interest payable on the floating rate notes. For the avoidance of doubt, in accordance with the benchmark replacement provisions, after a Benchmark Transition Event and its related Benchmark Replacement Date have occurred, the interest rate for each interest period on the floating rate notes will be an annual rate equal to the sum of the Benchmark Replacement (as defined below) and the applicable margin (not to be less than zero).

SOFR Index Unavailable

If a SOFR IndexStart or SOFR IndexEnd is not published on the associated interest determination date and a Benchmark Transition Event and its related Benchmark Replacement Date have not occurred with respect to the Secured Overnight Financing Rate,

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“Compounded SOFR” means, for the applicable interest period for which such index is not available, the rate of return on a daily compounded interest investment calculated in accordance with the formula for SOFR Averages, and definitions required for such formula, published on the New York Federal Reserve’s Website at https://www.newyorkfed.org/markets/treasury-repo-reference-rates-information. For the purposes of this provision, references in the SOFR Averages compounding formula and related definitions to “calculation period” shall be replaced with “Observation Period” and the words “that is, 30-, 90-, or 180- calendar days” shall be removed. If the daily Secured Overnight Financing Rate (“SOFRi”) does not so appear for any day, “i” in the Observation Period, SOFRi for such day “i” shall be SOFR published in respect of the first preceding U.S. Government Securities Business Day for which the Secured Overnight Financing Rate was published on the New York Federal Reserve’s Website.

Effect of a Benchmark Transition Event

If the Company or its designee determines on or prior to the relevant Reference Time that a Benchmark Transition Event and its related Benchmark Replacement Date have occurred with respect to the then-current Benchmark, the Benchmark Replacement will replace the then-current Benchmark for all purposes relating to the floating rate notes in respect of all determinations on such date and for all determinations on all subsequent dates.

In connection with the implementation of a Benchmark Replacement, the Company or its designee will have the right to make Benchmark Replacement Conforming Changes from time to time.

Any determination, decision or election that may be made by the Company or its designee pursuant to this section, including a determination with respect to a tenor, rate or adjustment or of the occurrence or non-occurrence of an event, circumstance or date and any decision to take or refrain from taking any action or any selection:

(1) will be conclusive and binding absent manifest error;

(2) if made by the Company, will be made in its sole discretion;

(4) notwithstanding anything to the contrary herein, in the Indenture or in the other documentation relating to this Security, shall become effective without consent from the holders of this Security or any other party.

As used herein, the following terms have the meanings assigned to them:

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occurred with respect to Compounded SOFR (or the published daily SOFR Index used in the calculation thereof) or the then-current Benchmark, then “Benchmark” means the applicable Benchmark Replacement.

“Benchmark Replacement” means the first alternative set forth in the order below that can be determined by the Company or its designee as of the Benchmark Replacement Date:

(2) the sum of (a) the ISDA Fallback Rate and (b) the Benchmark Replacement Adjustment; or

(3) the sum of (a) the alternate rate of interest that has been selected by the Company or its as the replacement for the then-current Benchmark giving due consideration to any industry-accepted rate of interest as a replacement for the then-current Benchmark for U.S. dollar-denominated floating rate notes at such time and (b) the Benchmark Replacement Adjustment

“Benchmark Replacement Adjustment” means the first alternative set forth in the order below that can be determined by the Company or its designee as of the Benchmark Replacement Date:

(2) if the applicable Unadjusted Benchmark Replacement is equivalent to the ISDA Fallback Rate, the ISDA Fallback Adjustment; or

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making payments of interest, rounding of amounts or tenors and other technical, administrative or operational matters) that the Company or its designee decides may be appropriate to reflect the adoption of such Benchmark Replacement in a manner substantially consistent with market practice (or, if the Company or its designee decides that adoption of any portion of such market practice is not administratively feasible or if the Company or its designee determines that no market practice for use of the Benchmark Replacement exists, in such other manner as the Company or its designee determines is reasonably practicable).

(2) in the case of clause (3) of the definition of “Benchmark Transition Event,” the date of the public statement or publication of information referenced therein.

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or a court or an entity with similar insolvency or resolution authority over the administrator for the Benchmark (or such component), which states that the administrator of the Benchmark (or such component) has ceased or will cease to provide the Benchmark (or such component) permanently or indefinitely; provided that, at the time of such statement or publication, there is no successor administrator that will continue to provide the Benchmark (or such component); or

(3) a public statement or publication of information by the regulatory supervisor for the administrator of the Benchmark announcing that the Benchmark is no longer representative.

“Unadjusted Benchmark Replacement” means the Benchmark Replacement excluding the Benchmark Replacement Adjustment.

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index, or (iv) to determine whether or what Benchmark Replacement Conforming Changes are necessary or advisable, if any, in connection with any of the foregoing. In connection with the foregoing, each of the trustee, the paying agent and the calculation agent shall be entitled to conclusively rely on any determinations made by the Company or its designee without independent investigation, and none will have any liability for actions taken at the Company’s direction in connection therewith.

None of the trustee, the paying agent or the calculation agent shall be liable for any inability, failure or delay on its part to perform any of its duties set forth in the Indenture or the Securities as a result of the unavailability of SOFR, the SOFR Index or other applicable Benchmark Replacement, including as a result of any failure, inability, delay, error or inaccuracy on the part of any other transaction party in providing any direction, instruction, notice or information required or contemplated by the terms of the Indenture or the Securities and reasonably required for the performance of such duties. In connection with any determination made hereunder, none of the trustee, the paying agent or the calculation agent shall be responsible or liable for the Company’s actions or omissions or for those of its designee, or for any failure or delay in the performance by the Company or its designee, nor shall any of the trustee, the paying agent or the calculation agent be under any obligation to oversee or monitor the Company’s performance or that of its designee.

If an Event of Default with respect to the Securities of this series shall occur and be continuing, the principal of the Securities of this series may be declared due and payable in the manner and with the effect provided in the Indenture.

The Indenture contains provisions for defeasance at any time of (i) the entire indebtedness of this Security or (ii) certain restrictive covenants and Events of Default with respect to this Security, in each case upon compliance with certain conditions set forth therein.

The Indenture permits, with certain exceptions as therein provided, the amendment thereof and the modification of the rights and obligations of the Company and the rights of the Holders of the Securities of each series to be affected under the Indenture at any time by the Company and the Trustee with the consent of the Holders of a majority in principal amount of the Securities at the time Outstanding of each series to be affected. The Indenture also contains provisions permitting the Holders of specified percentages in principal amount of the Securities of each series at the time Outstanding, on behalf of the Holders of all Securities of such series, to waive compliance by the Company with certain provisions of the Indenture and certain past defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Security shall be conclusive and binding upon such Holder and upon all future Holders of this Security and of any Security issued upon the registration of transfer hereof or in exchange thereof or in lieu hereof, whether or not notation of such consent or waiver is made upon this Security.

No reference herein to the Indenture and no provision of this Security or of the Indenture shall alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of and any premium and interest on this Security at the times, place and rate, and in the coin or currency, herein prescribed.

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As provided in the Indenture and subject to certain limitations therein set forth, the transfer of this Security is registrable in the Security Register, upon surrender of this Security for registration of transfer at the office or agency of the Company in any place where the principal of (and premium, if any) and interest on this Security are payable, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Security Registrar duly executed by, the Holder hereof or his attorney duly authorized in writing, and thereupon one or more new Securities of this series and of like tenor, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees.

The Securities of this series are issuable only in registered form without coupons in denominations of $2,000 and integral multiples of $1,000 in excess thereof. As provided in the Indenture and subject to certain limitations therein set forth, Securities of this series are exchangeable for a like aggregate principal amount of Securities of this series and of like tenor of a different authorized denomination, as requested by the Holder surrendering the same.

No service charge shall be made for any such registration of transfer or exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith.

Prior to due presentment of this Security for registration of transfer, the Company, the Trustee and any agent of the Company or the Trustee may treat the Person in whose name this Security is registered as the owner hereof for all purposes, whether or not this Security be overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary.

All terms used in this Security which are defined in the Indenture shall have the meanings assigned to them in the Indenture.

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ABBREVIATIONS

The following abbreviations, when used in the inscription on the face of the within Security, shall be construed as though they were written out in full according to applicable laws or regulations.

TEN COM - as tenants in common

TEN ENT - as tenants by the entireties

JT TEN - as joint tenants with right of survivorship and not as tenants in common

UNIF GIFT MIN ACT -

Custodian

(Cust)

(Minor)

under Uniform Gifts to Minors Act

(State)

Additional abbreviations may also be used
though not in the above list.

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ASSIGNMENT

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto _________________________________________________________________

PLEASE INSERT SOCIAL SECURITY OR OTHER

IDENTIFYING NUMBER OF ASSIGNEE






			(Please Print or Typewrite Name and Address, Including Postal Zip Code, of Assignee)


			the within Security and all rights thereunder, and hereby irrevocably constitutes and
			appoints

to transfer said Security on the books of the Company, with full power of substitution in the premises.

Dated: __________________

Signature Guaranteed

NOTICE: Signature must be guaranteed by a member firm of the New York Stock Exchange or a commercial bank or trust company.

NOTICE: The signature to this assignment must correspond with the name as written upon the face of the within Security in every particular, without alteration or enlargement or any change whatever.

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Exhibit 4.2

3.850% NOTES DUE 2027

MERCK & CO., INC.

Officers’ Certificate

Pursuant to the unanimous written consent and resolutions (collectively, the “Resolutions”) of the Board of Directors of Merck & Co., Inc. (the “Company”) (i) duly adopted and dated March 14, 2024 and (ii) adopted at a meeting duly called and held on November 30, 2021 (at which meeting a quorum was present and acting throughout), which authorized the Company to issue and sell its debt securities and empowered an Authorized Officer (as defined in the Resolutions) to approve the form and terms of such debt securities, Melissa Leonard, Senior Vice President and Treasurer and Kelly E. W. Grez, Corporate Secretary, each hereby approves and establishes under the Indenture, dated as of January 6, 2010 (the “Indenture”), between the Company and U.S. Bank Trust National Association, as Trustee (the “Trustee”), a series of debt securities the terms of which are as follows:

1. The title of the debt securities of such series shall be 3.850% Notes due 2027 (the “2027 Notes”).

2. The aggregate principal amount of the 2027 Notes which may be authenticated and delivered under the Indenture is initially limited to $750,000,000, except for 2027 Notes authenticated and delivered upon registration or transfer of, or in exchange for, or in lieu of, other 2027 Notes of the series pursuant to Section 304, 305, 306, 906 or 1107 of the Indenture and except for any 2027 Notes which, pursuant to Section 303 of the Indenture, are deemed never to have been authenticated and delivered under the Indenture.

3. The Company shall have the right from time to time, without the consent of the Holders of the 2027 Notes, to create and issue additional notes with the same terms and conditions as the 2027 Notes except for the issue date, issue price and the first payment of interest thereon (“Additional Notes”), provided that if the Additional Notes are not fungible with the previously outstanding 2027 Notes for U.S. federal income tax purposes, such Additional Notes will have a separate CUSIP. Additional Notes will be consolidated with and will form a single series with the previously outstanding 2027 Notes. Any election by the Company to so increase such aggregate principal amount shall be evidenced by a certificate of an Authorized

Officer or Authorized Officers. No Additional Notes may be issued if an Event of Default has occurred or is continuing with respect to the 2027 Notes.

4. The 2027 Notes shall be issued in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

5. The proceeds to the Company (after deducting the underwriting discounts and commissions but before deducting certain expenses payable by the Company in connection with the issuance of the 2027 Notes) shall be 99.755% of the aggregate principal amount of the 2027 Notes.

6. The maturity date on which the principal of each of the 2027 Notes is payable shall be September 15, 2027.

7. The 2027 Notes shall bear interest at the rate of 3.850% per annum from (and including) September 9, 2025. Interest shall be payable on each Interest Payment Date and at the maturity date. Interest payments shall be in the amount of interest accrued to, but excluding, the relevant Interest Payment Date or the maturity date, as applicable.

8. The Interest Payment Dates for the 2027 Notes shall be March 15 and September 15 of each year, commencing on March 15, 2026, and the Regular Record Dates for the 2027 Notes shall be the preceding March 1 or September 1, as the case may be.

If any payment date for the 2027 Notes is not a business day, the Company will make the payment on the next business day, but the Company will not be liable for any additional interest as a result of the delay in payment. With respect to the 2027 Notes, business day means any Monday, Tuesday, Wednesday, Thursday or Friday which is not a day when banking institutions in the place of payment are authorized or obligated by law or executive order to be closed.

9. Prior to the maturity date, the Company may redeem the 2027 Notes at its option, in whole or in part, at any time and from time to time, at a Redemption Price (expressed as a percentage of principal amount and rounded to three decimal places) equal to the greater of:

(1) (a) the sum of the present values of the remaining scheduled payments of principal and interest on the 2027 Notes to be redeemed discounted to the Redemption Date (assuming the 2027 Notes matured on the maturity date) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 5 basis points less (b) interest accrued to, but excluding, the Redemption Date, and

(2) 100% of the principal amount of the 2027 Notes to be redeemed,

plus, in either case, accrued and unpaid interest thereon to, but excluding, the Redemption Date.

“Treasury Rate” means, with respect to any Redemption Date, as applicable, the yield determined by the Company in accordance with the following two paragraphs.

The Treasury Rate shall be determined by the Company after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the Redemption Date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading). In determining the Treasury Rate, the Company shall select, as applicable: (1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the Redemption Date to the maturity date of the 2027 Notes to be redeemed (the “Remaining Life”); or (2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields – one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life – and shall interpolate to the maturity date of the 2027 Notes to be redeemed on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or (3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the Redemption Date.

If on the third business day preceding the Redemption Date H.15 or any successor designation or publication is no longer published, the Company shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second business day preceding such Redemption Date of the United States Treasury security maturing on, or with a maturity that is closest to, the maturity date of the 2027 Notes to be redeemed. If there is no United States Treasury security maturing on the maturity date of the 2027 Notes to be redeemed but there are two or more United States Treasury securities with a maturity date equally distant from such maturity date of the 2027 Notes to be redeemed, one with a maturity date preceding such maturity date of the 2027 Notes to be redeemed and one with a maturity date following such maturity date of the 2027 Notes to be redeemed, the Company shall select the United States Treasury security with a maturity date preceding such maturity date of the 2027 Notes to be redeemed. If there are two or more United States Treasury securities maturing on the maturity date of the 2027 Notes to be redeemed or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Company shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time on such day. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal amount) at 11:00 a.m., New York City time on such day, of such United States Treasury security, and rounded to three decimal places.

The Company’s actions and determinations in determining the Redemption Price shall be conclusive and binding for all purposes, absent manifest error.

Notice of any such redemption will be mailed or electronically delivered (or otherwise transmitted in accordance with the depositary’s procedures) at least 10 days but not more than 60 days before the Redemption Date to each Holder of 2027 Notes to be redeemed.

In the case of a partial redemption of the 2027 Notes, selection of the 2027 Notes for redemption will be made pro rata, by lot or by such other method as the Trustee in its sole discretion deems appropriate and fair. No 2027 Notes of a principal amount of $2,000 or less will be redeemed in part. If any 2027 Note is to be redeemed in part only, the notice of redemption that relates to the 2027 Note will state the portion of the principal amount of the 2027 Note to be redeemed. A new 2027 Note in a principal amount equal to the unredeemed portion of the 2027 Note will be issued in the name of the Holder of the 2027 Note upon surrender for cancellation of the original 2027 Note. For so long as the 2027 Notes to be redeemed are held by The Depository Trust Company (“DTC”) (or another depositary), the redemption of the 2027 Notes shall be done in accordance with the policies and procedures of the depositary.

Unless the Company defaults in payment of the Redemption Price, on and after the Redemption Date interest will cease to accrue on the 2027 Notes or portions thereof called for redemption.

10. Payment of the principal and interest on the 2027 Notes will be made at the office or agency of the Company maintained for that purpose in New York, New York (initially, the Corporate Trust Office of the Trustee), provided that at the option of the Company payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Security Register.

11. The provisions on defeasance and covenant defeasance in Article Thirteen of the Indenture shall apply to the 2027 Notes.

12. The 2027 Notes shall be issued in the form of one or more Book-Entry Securities and the Depository for such Book-Entry Securities shall be The Depository Trust Company, Clearstream Banking societé anonyme and Euroclear Bank SA/NV.

13. The form of the 2027 Notes attached hereto as Annex A is hereby approved.

Capitalized terms used herein and not otherwise defined herein have the meanings specified in the Indenture.

IN WITNESS WHEREOF, we have hereunto signed our names this ninth day of September, 2025.


			/s/ Melissa Leonard
			Name:			Melissa Leonard
			Title:			Senior Vice President and Treasurer


			/s/ Kelly E. W. Grez
			Name:			Kelly E. W. Grez
			Title:			Corporate Secretary

[Section 301 Officers’ Certificate – 2027 Notes]

Annex A

[FORM OF GLOBAL NOTES]


REGISTERED No. R-[1][2] CUSIP NO. 58933Y BP9			REGISTERED PRINCIPAL AMOUNT: $[●]1

MERCK & CO., INC.

3.850% NOTES DUE 2027

1 On September 9, 2025, the 2027 Notes will be issued in the form of two Book-Entry Securities in the principal amounts of $500,000,000 and $250,000,000.

A-2

Merck & Co., Inc., a New Jersey corporation (hereinafter called the “Company”, which term includes any successor corporation under the Indenture hereinafter referred to), for value received, hereby promises to pay to Cede & Co., as nominee for The Depository Trust Company, or registered assigns, the principal sum of [●] Hundred Million Dollars ($[●]) on September 15, 2027 and to pay interest thereon from and including September 9, 2025 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually in arrears on March 15 and September 15 in each year and at Maturity, commencing on March 15, 2026, at a rate per annum of 3.850%, until the principal hereof is paid or made available for payment, and (to the extent that the payment of such interest shall be legally enforceable) at the interest rate specified above on any overdue principal and premium and on any overdue installment of interest. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be the March 1 or September 1 (whether or not a Business Day in New York City), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Securities of this series may be listed, and upon such notice as may be required by such exchange, all as more fully provided in said Indenture.

A-3

[Signature page follows]

A-4

IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed under its corporate seal.

Dated: September 9, 2025


			MERCK & CO., INC.

			By:
						Name:
						Title:


Attest:

By:

Name:
Title:

A-5

CERTIFICATE OF AUTHENTICATION

This is one of the Securities of the series designated herein referred to in the within-mentioned Indenture.


U.S. BANK TRUST NATIONAL ASSOCIATION, As Trustee


By:
			Authorized Officer

A-6

[REVERSE OF SECURITY]

MERCK & CO., INC.

3.850% NOTES DUE 2027

This Security is one of the series designated on the face hereof. The aggregate principal amount of such series is $750,000,000 provided that the Company may increase such aggregate principal amount at any time.

Payments of interest hereon with respect to any Interest Payment Date will include interest accrued to but excluding such Interest Payment Date. Interest hereon shall be computed on the basis of a 360-day year consisting of twelve 30-day months.

This Security is not subject to any sinking fund.

A-7

Prior to the maturity date, the Company may redeem the Securities at its option, in whole or in part, at any time and from time to time, at a Redemption Price (expressed as a percentage of principal amount and rounded to three decimal places) equal to the greater of:

(1) (a) the sum of the present values of the remaining scheduled payments of principal and interest on the Securities to be redeemed discounted to the Redemption Date (assuming the Securities matured on the maturity date) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 5 basis points less (b) interest accrued to, but excluding, the Redemption Date, and

(2) 100% of the principal amount of the Securities to be redeemed,

plus, in either case, accrued and unpaid interest thereon to, but excluding, the Redemption Date.

“Treasury Rate” means, with respect to any Redemption Date, as applicable, the yield determined by the Company in accordance with the following two paragraphs.

The Treasury Rate shall be determined by the Company after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the Redemption Date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading). In determining the Treasury Rate, the Company shall select, as applicable: (1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the Redemption Date to the maturity date of the Securities to be redeemed (the “Remaining Life”); or (2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields – one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life – and shall interpolate to the maturity date of the Securities to be redeemed on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or (3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the Redemption Date.

A-8

date of the Securities to be redeemed but there are two or more United States Treasury securities with a maturity date equally distant from such maturity date of the Securities to be redeemed, one with a maturity date preceding such maturity date of the Securities to be redeemed and one with a maturity date following such maturity date of the Securities to be redeemed, the Company shall select the United States Treasury security with a maturity date preceding such maturity date of the Securities to be redeemed. If there are two or more United States Treasury securities maturing on the maturity date of the Securities to be redeemed or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Company shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time on such day. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal amount) at 11:00 a.m., New York City time on such day, of such United States Treasury security, and rounded to three decimal places.

The Company’s actions and determinations in determining the Redemption Price shall be conclusive and binding for all purposes, absent manifest error.

In the case of a partial redemption of the Securities, selection of the Securities for redemption will be made pro rata, by lot or by such other method as the Trustee in its sole discretion deems appropriate and fair. No Securities of a principal amount of $2,000 or less will be redeemed in part. If any Security is to be redeemed in part only, the notice of redemption that relates to the Security will state the portion of the principal amount of the Security to be redeemed. A new Security in a principal amount equal to the unredeemed portion of the Security will be issued in the name of the Holder of the Security upon surrender for cancellation of the original Security. For so long as the Securities to be redeemed are held by DTC (or another depositary), the redemption of the Securities shall be done in accordance with the policies and procedures of the depositary.

Unless the Company defaults in payment of the Redemption Price, on and after the Redemption Date interest will cease to accrue on the Securities or portions thereof called for redemption.

A-9

A-10

All terms used in this Security which are defined in the Indenture shall have the meanings assigned to them in the Indenture.

A-11

ABBREVIATIONS

The following abbreviations, when used in the inscription on the face of the within Security, shall be construed as though they were written out in full according to applicable laws or regulations.


TEN COM	-	as tenants in common

TEN ENT	-	as tenants by the entireties

JT TEN	-	as joint tenants with right of survivorship and not as tenants in common

UNIF GIFT MIN ACT -

Custodian

(Cust)

(Minor)


						under Uniform Gifts to Minors Act

						(State)



						Additional abbreviations may also be used though not in the above list.

A-12

ASSIGNMENT

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto _________________________________________________________________

PLEASE INSERT SOCIAL SECURITY OR OTHER

IDENTIFYING NUMBER OF ASSIGNEE







			(Please Print or Typewrite Name and Address, Including Postal Zip Code, of Assignee)


			the within Security and all rights thereunder, and hereby irrevocably constitutes and
			appoints

to transfer said Security on the books of the Company, with full power of substitution in the premises.

Dated: __________________

Signature Guaranteed

NOTICE: Signature must be guaranteed by a member firm of the New York Stock Exchange or a commercial bank or trust company.

NOTICE: The signature to this assignment must correspond with the name as written upon the face of the within Security in every particular, without alteration or enlargement or any change whatever.

A-13

Exhibit 4.3

4.150% NOTES DUE 2030

MERCK & CO., INC.

Officers’ Certificate

Pursuant to the unanimous written consent and resolutions (collectively, the “Resolutions”) of the Board of Directors of Merck & Co., Inc. (the “Company”) (i) duly adopted and dated March 14, 2024 and (ii) adopted at a meeting duly called and held on November 30, 2021 (at which meeting a quorum was present and acting throughout), which authorized the Company to issue and sell its debt securities and empowered an Authorized Officer (as defined in the Resolutions) to approve the form and terms of such debt securities, Melissa Leonard, Senior Vice President and Treasurer and Kelly E. W. Grez, Corporate Secretary, each hereby approves and establishes under the Indenture, dated as of January 6, 2010 (the “Indenture”), between the Company and U.S. Bank Trust National Association, as Trustee (the “Trustee”), a series of debt securities the terms of which are as follows:

1. The title of the debt securities of such series shall be 4.150% Notes due 2030 (the “2030 Notes”).

2. The aggregate principal amount of the 2030 Notes which may be authenticated and delivered under the Indenture is initially limited to $750,000,000, except for 2030 Notes authenticated and delivered upon registration or transfer of, or in exchange for, or in lieu of, other 2030 Notes of the series pursuant to Section 304, 305, 306, 906 or 1107 of the Indenture and except for any 2030 Notes which, pursuant to Section 303 of the Indenture, are deemed never to have been authenticated and delivered under the Indenture.

3. The Company shall have the right from time to time, without the consent of the Holders of the 2030 Notes, to create and issue additional notes with the same terms and conditions as the 2030 Notes except for the issue date, issue price and the first payment of interest thereon (“Additional Notes”), provided that if the Additional Notes are not fungible with the previously outstanding 2030 Notes for U.S. federal income tax purposes, such Additional Notes will have a separate CUSIP. Additional Notes will be consolidated with and will form a single series with the previously outstanding 2030 Notes. Any election by the Company to so increase such aggregate principal amount shall be evidenced by a certificate of an Authorized Officer or Authorized Officers. No Additional Notes may be issued if an Event of Default has occurred or is continuing with respect to the 2030 Notes.

4. The 2030 Notes shall be issued in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

5. The proceeds to the Company (after deducting the underwriting discounts and commissions but before deducting certain expenses payable by the Company in connection with the issuance of the 2030 Notes) shall be 99.483% of the aggregate principal amount of the 2030 Notes.

6. The maturity date on which the principal of each of the 2030 Notes is payable shall be September 15, 2030.

7. The 2030 Notes shall bear interest at the rate of 4.150% per annum from (and including) September 9, 2025. Interest shall be payable on each Interest Payment Date and at the maturity date. Interest payments shall be in the amount of interest accrued to, but excluding, the relevant Interest Payment Date or the maturity date, as applicable.

8. The Interest Payment Dates for the 2030 Notes shall be March 15 and September 15 of each year, commencing on March 15, 2026, and the Regular Record Dates for the 2030 Notes shall be the preceding March 1 or September 1, as the case may be.

If any payment date for the 2030 Notes is not a business day, the Company will make the payment on the next business day, but the Company will not be liable for any additional interest as a result of the delay in payment. With respect to the 2030 Notes, business day means any Monday, Tuesday, Wednesday, Thursday or Friday which is not a day when banking institutions in the place of payment are authorized or obligated by law or executive order to be closed.

9. Prior to the Par Call Date, the Company may redeem the 2030 Notes at its option, in whole or in part, at any time and from time to time, at a Redemption Price (expressed as a percentage of principal amount and rounded to three decimal places) equal to the greater of:

(1) (a) the sum of the present values of the remaining scheduled payments of principal and interest on the 2030 Notes to be redeemed discounted to the Redemption Date (assuming the 2030 Notes matured on the Par Call Date) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 10 basis points less (b) interest accrued to, but excluding, the Redemption Date, and

(2) 100% of the principal amount of the 2030 Notes to be redeemed,

plus, in either case, accrued and unpaid interest thereon to, but excluding, the Redemption Date.

On or after the Par Call Date, the Company may redeem the 2030 Notes in whole or in part, at any time and from time to time, at a Redemption Price equal to 100% of the principal amount of the 2030 Notes being redeemed plus accrued and unpaid interest thereon to, but excluding, the Redemption Date.

“Par Call Date” means August 15, 2030, the date that is one month prior to the maturity of the 2030 Notes.

“Treasury Rate” means, with respect to any Redemption Date, as applicable, the yield determined by the Company in accordance with the following two paragraphs.

The Treasury Rate shall be determined by the Company after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the Redemption Date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading). In determining the Treasury Rate, the Company shall select, as applicable: (1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the Redemption Date to the Par Call Date of the 2030 Notes to be redeemed (the “Remaining Life”); or (2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields – one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life – and shall interpolate to the Par Call Date of the 2030 Notes to be redeemed on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or (3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the Redemption Date.

If on the third business day preceding the Redemption Date H.15 or any successor designation or publication is no longer published, the Company shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second business day preceding such Redemption Date of the United States Treasury security maturing on, or with a maturity that is closest to, the Par Call Date of the 2030 Notes to be redeemed. If there is no United States Treasury security maturing on the Par Call Date of the 2030 Notes to be redeemed but there are two or more United States Treasury securities with a maturity date equally distant from such Par Call Date of the 2030 Notes to be redeemed, one with a maturity date preceding such Par Call Date of the 2030 Notes to be redeemed and one with a maturity date following such Par Call Date of the 2030 Notes to be redeemed, the Company shall select the United States Treasury security with a maturity date preceding such Par Call Date of the 2030 Notes to be redeemed. If there are two or more United States Treasury securities maturing on the Par Call Date of the 2030 Notes to be redeemed or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Company shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time on such day. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be

based upon the average of the bid and asked prices (expressed as a percentage of principal amount) at 11:00 a.m., New York City time on such day, of such United States Treasury security, and rounded to three decimal places.

The Company’s actions and determinations in determining the Redemption Price shall be conclusive and binding for all purposes, absent manifest error.

In the case of a partial redemption of the 2030 Notes, selection of the 2030 Notes for redemption will be made pro rata, by lot or by such other method as the Trustee in its sole discretion deems appropriate and fair. No 2030 Notes of a principal amount of $2,000 or less will be redeemed in part. If any 2030 Note is to be redeemed in part only, the notice of redemption that relates to the 2030 Note will state the portion of the principal amount of the 2030 Note to be redeemed. A new 2030 Note in a principal amount equal to the unredeemed portion of the 2030 Note will be issued in the name of the Holder of the 2030 Note upon surrender for cancellation of the original 2030 Note. For so long as the 2030 Notes to be redeemed are held by The Depository Trust Company (“DTC”) (or another depositary), the redemption of the 2030 Notes shall be done in accordance with the policies and procedures of the depositary.

Unless the Company defaults in payment of the Redemption Price, on and after the Redemption Date interest will cease to accrue on the 2030 Notes or portions thereof called for redemption.

10. Payment of the principal and interest on the 2030 Notes will be made at the office or agency of the Company maintained for that purpose in New York, New York (initially, the Corporate Trust Office of the Trustee), provided that at the option of the Company payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Security Register.

11. The provisions on defeasance and covenant defeasance in Article Thirteen of the Indenture shall apply to the 2030 Notes.

12. The 2030 Notes shall be issued in the form of one or more Book-Entry Securities and the Depository for such Book-Entry Securities shall be The Depository Trust Company, Clearstream Banking societé anonyme and Euroclear Bank SA/NV.

13. The form of the 2030 Notes attached hereto as Annex A is hereby approved.

Capitalized terms used herein and not otherwise defined herein have the meanings specified in the Indenture.

IN WITNESS WHEREOF, we have hereunto signed our names this ninth day of September, 2025.


			/s/ Melissa Leonard
			Name:			Melissa Leonard
			Title:			Senior Vice President and Treasurer


			/s/ Kelly E. W. Grez
			Name:			Kelly E. W. Grez
			Title:			Corporate Secretary

[Section 301 Officers’ Certificate – 2030 Notes]

Annex A

[FORM OF GLOBAL NOTES]


REGISTERED			REGISTERED
No. R-[1][2]			PRINCIPAL AMOUNT: $[●]1
CUSIP NO. 58933Y BQ7

MERCK & CO., INC.

4.150% NOTES DUE 2030

1 On September 9, 2025, the 2030 Notes will be issued in the form of two Book-Entry Securities in the principal amounts of $500,000,000 and $250,000,000.

A-2

Merck & Co., Inc., a New Jersey corporation (hereinafter called the “Company”, which term includes any successor corporation under the Indenture hereinafter referred to), for value received, hereby promises to pay to Cede & Co., as nominee for The Depository Trust Company, or registered assigns, the principal sum of [●] Hundred Million Dollars ($[●]) on September 15, 2030 and to pay interest thereon from and including September 9, 2025 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually in arrears on March 15 and September 15 in each year and at Maturity, commencing on March 15, 2026, at a rate per annum of 4.150%, until the principal hereof is paid or made available for payment, and (to the extent that the payment of such interest shall be legally enforceable) at the interest rate specified above on any overdue principal and premium and on any overdue installment of interest. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be the March 1 or September 1 (whether or not a Business Day in New York City), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Securities of this series may be listed, and upon such notice as may be required by such exchange, all as more fully provided in said Indenture.

A-3

[Signature page follows]

A-4

IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed under its corporate seal.

Dated: September 9, 2025

MERCK & CO., INC.

By:

Name:

Title:

Attest:

By:

Name:

Title:

A-5

CERTIFICATE OF AUTHENTICATION

This is one of the Securities of the series designated herein referred to in the within-mentioned Indenture.


U.S. BANK TRUST NATIONAL ASSOCIATION, As Trustee


By:
			Authorized Officer

A-6

[REVERSE OF SECURITY]

MERCK & CO., INC.

4.150% NOTES DUE 2030

This Security is not subject to any sinking fund.

A-7

Prior to the Par Call Date, the Company may redeem the Securities at its option, in whole or in part, at any time and from time to time, at a Redemption Price (expressed as a percentage of principal amount and rounded to three decimal places) equal to the greater of:

(1) (a) the sum of the present values of the remaining scheduled payments of principal and interest on the Securities to be redeemed discounted to the Redemption Date (assuming the Securities matured on the Par Call Date) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 10 basis points less (b) interest accrued to, but excluding, the Redemption Date, and

(2) 100% of the principal amount of the Securities to be redeemed,

plus, in either case, accrued and unpaid interest thereon to, but excluding, the Redemption Date.

On or after August 15, 2030 (one month prior to the Stated Maturity of the Securities, or the “Par Call Date”), the Company may redeem the Securities in whole or in part, at any time and from time to time, at a Redemption Price equal to 100% of the principal amount of the Securities being redeemed plus accrued and unpaid interest thereon to, but excluding, the Redemption Date.

“Treasury Rate” means, with respect to any Redemption Date, as applicable, the yield determined by the Company in accordance with the following two paragraphs.

The Treasury Rate shall be determined by the Company after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the Redemption Date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading). In determining the Treasury Rate, the Company shall select, as applicable: (1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the Redemption Date to the Par Call Date of the Securities to be redeemed (the “Remaining Life”); or (2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields – one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life – and shall interpolate to the Par Call Date of the Securities to be redeemed on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or (3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the Redemption Date.

A-8

If on the third business day preceding the Redemption Date H.15 or any successor designation or publication is no longer published, the Company shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second business day preceding such Redemption Date of the United States Treasury security maturing on, or with a maturity that is closest to, the Par Call Date of the Securities to be redeemed. If there is no United States Treasury security maturing on the Par Call Date of the Securities to be redeemed but there are two or more United States Treasury securities with a maturity date equally distant from such Par Call Date of the Securities to be redeemed, one with a maturity date preceding such Par Call Date of the Securities to be redeemed and one with a maturity date following such Par Call Date of the Securities to be redeemed, the Company shall select the United States Treasury security with a maturity date preceding such Par Call Date of the Securities to be redeemed. If there are two or more United States Treasury securities maturing on the Par Call Date of the Securities to be redeemed or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Company shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time on such day. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal amount) at 11:00 a.m., New York City time on such day, of such United States Treasury security, and rounded to three decimal places.

The Company’s actions and determinations in determining the Redemption Price shall be conclusive and binding for all purposes, absent manifest error.

Unless the Company defaults in payment of the Redemption Price, on and after the Redemption Date interest will cease to accrue on the Securities or portions thereof called for redemption.

A-9

A-10

All terms used in this Security which are defined in the Indenture shall have the meanings assigned to them in the Indenture.

A-11

ABBREVIATIONS

The following abbreviations, when used in the inscription on the face of the within Security, shall be construed as though they were written out in full according to applicable laws or regulations.


TEN COM	-	as tenants in common

TEN ENT	-	as tenants by the entireties

JT TEN	-	as joint tenants with right of survivorship and not as tenants in common

UNIF GIFT MIN ACT -

Custodian

(Cust)

(Minor)


						under Uniform Gifts to Minors Act

						(State)

						Additional abbreviations may also be used though not in the above list.

A-12

ASSIGNMENT

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto _________________________________________________________________

PLEASE INSERT SOCIAL SECURITY OR OTHER

IDENTIFYING NUMBER OF ASSIGNEE







			(Please Print or Typewrite Name and Address, Including Postal Zip Code, of Assignee)


			the within Security and all rights thereunder, and hereby irrevocably constitutes and
			appoints

to transfer said Security on the books of the Company, with full power of substitution in the premises.

Dated: __________________

Signature Guaranteed

NOTICE: Signature must be guaranteed by a member firm of the New York Stock Exchange or a commercial bank or trust company.

NOTICE: The signature to this assignment must correspond with the name as written upon the face of the within Security in every particular, without alteration or enlargement or any change whatever.

A-13

Exhibit 4.4

4.550% NOTES DUE 2032

MERCK & CO., INC.

Officers’ Certificate

Pursuant to the unanimous written consent and resolutions (collectively, the “Resolutions”) of the Board of Directors of Merck & Co., Inc. (the “Company”) (i) duly adopted and dated March 14, 2024 and (ii) adopted at a meeting duly called and held on November 30, 2021 (at which meeting a quorum was present and acting throughout), which authorized the Company to issue and sell its debt securities and empowered an Authorized Officer (as defined in the Resolutions) to approve the form and terms of such debt securities, Melissa Leonard, Senior Vice President and Treasurer and Kelly E. W. Grez, Corporate Secretary, each hereby approves and establishes under the Indenture, dated as of January 6, 2010 (the “Indenture”), between the Company and U.S. Bank Trust National Association, as Trustee (the “Trustee”), a series of debt securities the terms of which are as follows:

1. The title of the debt securities of such series shall be 4.550% Notes due 2032 (the “2032 Notes”).

2. The aggregate principal amount of the 2032 Notes which may be authenticated and delivered under the Indenture is initially limited to $1,000,000,000, except for 2032 Notes authenticated and delivered upon registration or transfer of, or in exchange for, or in lieu of, other 2032 Notes of the series pursuant to Section 304, 305, 306, 906 or 1107 of the Indenture and except for any 2032 Notes which, pursuant to Section 303 of the Indenture, are deemed never to have been authenticated and delivered under the Indenture.

3. The Company shall have the right from time to time, without the consent of the Holders of the 2032 Notes, to create and issue additional notes with the same terms and conditions as the 2032 Notes except for the issue date, issue price and the first payment of interest thereon (“Additional Notes”), provided that if the Additional Notes are not fungible with the previously outstanding 2032 Notes for U.S. federal income tax purposes, such Additional Notes will have a separate CUSIP. Additional Notes will be consolidated with and will form a single series with the previously outstanding 2032 Notes. Any election by the Company to so increase such aggregate principal amount shall be evidenced by a certificate of an Authorized Officer or Authorized Officers. No Additional Notes may be issued if an Event of Default has occurred or is continuing with respect to the 2032 Notes.

4. The 2032 Notes shall be issued in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

5. The proceeds to the Company (after deducting the underwriting discounts and commissions but before deducting certain expenses payable by the Company in connection with the issuance of the 2032 Notes) shall be 99.581% of the aggregate principal amount of the 2032 Notes.

6. The maturity date on which the principal of each of the 2032 Notes is payable shall be September 15, 2032.

7. The 2032 Notes shall bear interest at the rate of 4.550% per annum from (and including) September 9, 2025. Interest shall be payable on each Interest Payment Date and at the maturity date. Interest payments shall be in the amount of interest accrued to, but excluding, the relevant Interest Payment Date or the maturity date, as applicable.

8. The Interest Payment Dates for the 2032 Notes shall be March 15 and September 15 of each year, commencing on March 15, 2026, and the Regular Record Dates for the 2032 Notes shall be the preceding March 1 or September 1, as the case may be.

If any payment date for the 2032 Notes is not a business day, the Company will make the payment on the next business day, but the Company will not be liable for any additional interest as a result of the delay in payment. With respect to the 2032 Notes, business day means any Monday, Tuesday, Wednesday, Thursday or Friday which is not a day when banking institutions in the place of payment are authorized or obligated by law or executive order to be closed.

9. Prior to the Par Call Date, the Company may redeem the 2032 Notes at its option, in whole or in part, at any time and from time to time, at a Redemption Price (expressed as a percentage of principal amount and rounded to three decimal places) equal to the greater of:

(1) (a) the sum of the present values of the remaining scheduled payments of principal and interest on the 2032 Notes to be redeemed discounted to the Redemption Date (assuming the 2032 Notes matured on the Par Call Date) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 10 basis points less (b) interest accrued to, but excluding, the Redemption Date, and

(2) 100% of the principal amount of the 2032 Notes to be redeemed,

plus, in either case, accrued and unpaid interest thereon to, but excluding, the Redemption Date.

On or after the Par Call Date, the Company may redeem the 2032 Notes in whole or in part, at any time and from time to time, at a Redemption Price equal to 100% of the principal amount of the 2032 Notes being redeemed plus accrued and unpaid interest thereon to, but excluding, the Redemption Date.

“Par Call Date” means July 15, 2032, the date that is two months prior to the maturity of the 2032 Notes.

“Treasury Rate” means, with respect to any Redemption Date, as applicable, the yield determined by the Company in accordance with the following two paragraphs.

The Treasury Rate shall be determined by the Company after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the Redemption Date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading). In determining the Treasury Rate, the Company shall select, as applicable: (1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the Redemption Date to the Par Call Date of the 2032 Notes to be redeemed (the “Remaining Life”); or (2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields – one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life – and shall interpolate to the Par Call Date of the 2032 Notes to be redeemed on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or (3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the Redemption Date.

If on the third business day preceding the Redemption Date H.15 or any successor designation or publication is no longer published, the Company shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second business day preceding such Redemption Date of the United States Treasury security maturing on, or with a maturity that is closest to, the Par Call Date of the 2032 Notes to be redeemed. If there is no United States Treasury security maturing on the Par Call Date of the 2032 Notes to be redeemed but there are two or more United States Treasury securities with a maturity date equally distant from such Par Call Date of the 2032 Notes to be redeemed, one with a maturity date preceding such Par Call Date of the 2032 Notes to be redeemed and one with a maturity date following such Par Call Date of the 2032 Notes to be redeemed, the Company shall select the United States Treasury security with a maturity date preceding such Par Call Date of the 2032 Notes to be redeemed. If there are two or more United States Treasury securities maturing on the Par Call Date of the 2032 Notes to be redeemed or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Company shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time on such day. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal

amount) at 11:00 a.m., New York City time on such day, of such United States Treasury security, and rounded to three decimal places.

The Company’s actions and determinations in determining the Redemption Price shall be conclusive and binding for all purposes, absent manifest error.

In the case of a partial redemption of the 2032 Notes, selection of the 2032 Notes for redemption will be made pro rata, by lot or by such other method as the Trustee in its sole discretion deems appropriate and fair. No 2032 Notes of a principal amount of $2,000 or less will be redeemed in part. If any 2032 Note is to be redeemed in part only, the notice of redemption that relates to the 2032 Note will state the portion of the principal amount of the 2032 Note to be redeemed. A new 2032 Note in a principal amount equal to the unredeemed portion of the 2032 Note will be issued in the name of the Holder of the 2032 Note upon surrender for cancellation of the original 2032 Note. For so long as the 2032 Notes to be redeemed are held by The Depository Trust Company (“DTC”) (or another depositary), the redemption of the 2032 Notes shall be done in accordance with the policies and procedures of the depositary.

Unless the Company defaults in payment of the Redemption Price, on and after the Redemption Date interest will cease to accrue on the 2032 Notes or portions thereof called for redemption.

10. Payment of the principal and interest on the 2032 Notes will be made at the office or agency of the Company maintained for that purpose in New York, New York (initially, the Corporate Trust Office of the Trustee), provided that at the option of the Company payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Security Register.

11. The provisions on defeasance and covenant defeasance in Article Thirteen of the Indenture shall apply to the 2032 Notes.

12. The 2032 Notes shall be issued in the form of one or more Book-Entry Securities and the Depository for such Book-Entry Securities shall be The Depository Trust Company, Clearstream Banking societé anonyme and Euroclear Bank SA/NV.

13. The form of the 2032 Notes attached hereto as Annex A is hereby approved.

Capitalized terms used herein and not otherwise defined herein have the meanings specified in the Indenture.

IN WITNESS WHEREOF, we have hereunto signed our names this ninth day of September, 2025.


			/s/ Melissa Leonard
			Name:			Melissa Leonard
			Title:			Senior Vice President and Treasurer


			/s/ Kelly E. W. Grez
			Name:			Kelly E. W. Grez
			Title:			Corporate Secretary

[Section 301 Officers’ Certificate – 2032 Notes]

Annex A

[FORM OF GLOBAL NOTES]


REGISTERED No. R-[1][2] CUSIP NO. 58933Y BR			REGISTERED PRINCIPAL AMOUNT: $[●]1

MERCK & CO., INC.

4.550% NOTES DUE 2032

1 On September 9, 2025, the 2035 Notes will be issued in the form of four Book-Entry Securities in the principal amounts of $500,000,000, $500,000,000, $500,000,000 and $250,000,000.

A-2

Merck & Co., Inc., a New Jersey corporation (hereinafter called the “Company”, which term includes any successor corporation under the Indenture hereinafter referred to), for value received, hereby promises to pay to Cede & Co., as nominee for The Depository Trust Company, or registered assigns, the principal sum of [●] Hundred Million Dollars ($[●]) on September 15, 2032 and to pay interest thereon from and including September 9, 2025 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually in arrears on March 15 and September 15 in each year and at Maturity, commencing on March 15, 2026, at a rate per annum of 4.550%, until the principal hereof is paid or made available for payment, and (to the extent that the payment of such interest shall be legally enforceable) at the interest rate specified above on any overdue principal and premium and on any overdue installment of interest. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be the March 1 or September 1 (whether or not a Business Day in New York City), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Securities of this series may be listed, and upon such notice as may be required by such exchange, all as more fully provided in said Indenture.

A-3

[Signature page follows]

A-4

IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed under its corporate seal.

Dated: September 9, 2025

MERCK & CO., INC.

By:

Name:

Title:

Attest:

By:

Name:

Title:

A-5

CERTIFICATE OF AUTHENTICATION

This is one of the Securities of the series designated herein referred to in the within-mentioned Indenture.


U.S. BANK TRUST NATIONAL ASSOCIATION, As Trustee


By:
			Authorized Officer

A-6

[REVERSE OF SECURITY]

MERCK & CO., INC.

4.550% NOTES DUE 2032

This Security is one of the series designated on the face hereof. The aggregate principal amount of such series is $1,000,000,000 provided that the Company may increase such aggregate principal amount at any time.

This Security is not subject to any sinking fund.

A-7

(1) (a) the sum of the present values of the remaining scheduled payments of principal and interest on the Securities to be redeemed discounted to the Redemption Date (assuming the Securities matured on the Par Call Date) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 10 basis points less (b) interest accrued to, but excluding, the Redemption Date, and

(2) 100% of the principal amount of the Securities to be redeemed,

plus, in either case, accrued and unpaid interest thereon to, but excluding, the Redemption Date.

On or after July 15, 2032 (two months prior to the Stated Maturity of the Securities, or the “Par Call Date”), the Company may redeem the Securities in whole or in part, at any time and from time to time, at a Redemption Price equal to 100% of the principal amount of the Securities being redeemed plus accrued and unpaid interest thereon to, but excluding, the Redemption Date.

“Treasury Rate” means, with respect to any Redemption Date, as applicable, the yield determined by the Company in accordance with the following two paragraphs.

The Treasury Rate shall be determined by the Company after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the Redemption Date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading). In determining the Treasury Rate, the Company shall select, as applicable: (1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the Redemption Date to the Par Call Date of the Securities to be redeemed (the “Remaining Life”); or (2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields – one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life – and shall interpolate to the Par Call Date of the Securities to be redeemed on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or (3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the Redemption Date.

A-8

If on the third business day preceding the Redemption Date H.15 or any successor designation or publication is no longer published, the Company shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second business day preceding such Redemption Date of the United States Treasury security maturing on, or with a maturity that is closest to, the Par Call Date of the Securities to be redeemed. If there is no United States Treasury security maturing on the Par Call Date of the Securities to be redeemed but there are two or more United States Treasury securities with a maturity date equally distant from such Par Call Date of the Securities to be redeemed, one with a maturity date preceding such Par Call Date of the Securities to be redeemed and one with a maturity date following such Par Call Date of the Securities to be redeemed, the Company shall select the United States Treasury security with a maturity date preceding such Par Call Date of the Securities to be redeemed. If there are two or more United States Treasury securities maturing on the Par Call Date of the Securities to be redeemed or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Company shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time on such day. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal amount) at 11:00 a.m., New York City time on such day, of such United States Treasury security, and rounded to three decimal places.

The Company’s actions and determinations in determining the Redemption Price shall be conclusive and binding for all purposes, absent manifest error.

Unless the Company defaults in payment of the Redemption Price, on and after the Redemption Date interest will cease to accrue on the Securities or portions thereof called for redemption.

A-9

A-10

All terms used in this Security which are defined in the Indenture shall have the meanings assigned to them in the Indenture.

A-11

ABBREVIATIONS

The following abbreviations, when used in the inscription on the face of the within Security, shall be construed as though they were written out in full according to applicable laws or regulations.

TEN COM - as tenants in common

TEN ENT - as tenants by the entireties

JT TEN - as joint tenants with right of survivorship and not as tenants in common

UNIF GIFT MIN ACT -

Custodian

(Cust)

(Minor)


						under Uniform Gifts to Minors Act

						(State)

						Additional abbreviations may also be used though not in the above list.

A-12

ASSIGNMENT

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto _________________________________________________________________

PLEASE INSERT SOCIAL SECURITY OR OTHER

IDENTIFYING NUMBER OF ASSIGNEE





(Please Print or Typewrite Name and Address, Including Postal Zip Code, of Assignee)


the within Security and all rights thereunder, and hereby irrevocably constitutes and
appoints

to transfer said Security on the books of the Company, with full power of substitution in the premises.

Dated: __________________

Signature Guaranteed

NOTICE: Signature must be guaranteed by a member firm of the New York Stock Exchange or a commercial bank or trust company.

NOTICE: The signature to this assignment must correspond with the name as written upon the face of the within Security in every particular, without alteration or enlargement or any change whatever.

A-13

Exhibit 4.5

4.950% NOTES DUE 2035

MERCK & CO., INC.

Officers’ Certificate

Pursuant to the unanimous written consent and resolutions (collectively, the “Resolutions”) of the Board of Directors of Merck & Co., Inc. (the “Company”) (i) duly adopted and dated March 14, 2024 and (ii) adopted at a meeting duly called and held on November 30, 2021 (at which meeting a quorum was present and acting throughout), which authorized the Company to issue and sell its debt securities and empowered an Authorized Officer (as defined in the Resolutions) to approve the form and terms of such debt securities, Melissa Leonard, Senior Vice President and Treasurer and Kelly E. W. Grez, Corporate Secretary, each hereby approves and establishes under the Indenture, dated as of January 6, 2010 (the “Indenture”), between the Company and U.S. Bank Trust National Association, as Trustee (the “Trustee”), a series of debt securities the terms of which are as follows:

1. The title of the debt securities of such series shall be 4.950% Notes due 2035 (the “2035 Notes”).

2. The aggregate principal amount of the 2035 Notes which may be authenticated and delivered under the Indenture is initially limited to $1,750,000,000, except for 2035 Notes authenticated and delivered upon registration or transfer of, or in exchange for, or in lieu of, other 2035 Notes of the series pursuant to Section 304, 305, 306, 906 or 1107 of the Indenture and except for any 2035 Notes which, pursuant to Section 303 of the Indenture, are deemed never to have been authenticated and delivered under the Indenture.

3. The Company shall have the right from time to time, without the consent of the Holders of the 2035 Notes, to create and issue additional notes with the same terms and conditions as the 2035 Notes except for the issue date, issue price and the first payment of interest thereon (“Additional Notes”), provided that if the Additional Notes are not fungible with the previously outstanding 2035 Notes for U.S. federal income tax purposes, such Additional Notes will have a separate CUSIP. Additional Notes will be consolidated with and will form a single series with the previously outstanding 2035 Notes. Any election by the Company to so increase such aggregate principal amount shall be evidenced by a certificate of an Authorized

Officer or Authorized Officers. No Additional Notes may be issued if an Event of Default has occurred or is continuing with respect to the 2035 Notes.

4. The 2035 Notes shall be issued in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

5. The proceeds to the Company (after deducting the underwriting discounts and commissions but before deducting certain expenses payable by the Company in connection with the issuance of the 2035 Notes) shall be 99.541% of the aggregate principal amount of the 2035 Notes.

6. The maturity date on which the principal of each of the 2035 Notes is payable shall be September 15, 2035.

7. The 2035 Notes shall bear interest at the rate of 4.950% per annum from (and including) September 9, 2025. Interest shall be payable on each Interest Payment Date and at the maturity date. Interest payments shall be in the amount of interest accrued to, but excluding, the relevant Interest Payment Date or the maturity date, as applicable.

8. The Interest Payment Dates for the 2035 Notes shall be March 15 and September 15 of each year, commencing on March 15, 2026, and the Regular Record Dates for the 2035 Notes shall be the preceding March 1 or September 1, as the case may be.

If any payment date for the 2035 Notes is not a business day, the Company will make the payment on the next business day, but the Company will not be liable for any additional interest as a result of the delay in payment. With respect to the 2035 Notes, business day means any Monday, Tuesday, Wednesday, Thursday or Friday which is not a day when banking institutions in the place of payment are authorized or obligated by law or executive order to be closed.

9. Prior to the Par Call Date, the Company may redeem the 2035 Notes at its option, in whole or in part, at any time and from time to time, at a Redemption Price (expressed as a percentage of principal amount and rounded to three decimal places) equal to the greater of:

(1) (a) the sum of the present values of the remaining scheduled payments of principal and interest on the 2035 Notes to be redeemed discounted to the Redemption Date (assuming the 2035 Notes matured on the Par Call Date) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 15 basis points less (b) interest accrued to, but excluding, the Redemption Date, and

(2) 100% of the principal amount of the 2035 Notes to be redeemed,

plus, in either case, accrued and unpaid interest thereon to, but excluding, the Redemption Date.

On or after the Par Call Date, the Company may redeem the 2035 Notes in whole or in part, at any time and from time to time, at a Redemption Price equal to 100% of the principal amount of the 2035 Notes being redeemed plus accrued and unpaid interest thereon to, but excluding, the Redemption Date.

“Par Call Date” means June 15, 2035, the date that is three months prior to the maturity of the 2035 Notes.

“Treasury Rate” means, with respect to any Redemption Date, as applicable, the yield determined by the Company in accordance with the following two paragraphs.

The Treasury Rate shall be determined by the Company after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the Redemption Date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading). In determining the Treasury Rate, the Company shall select, as applicable: (1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the Redemption Date to the Par Call Date of the 2035 Notes to be redeemed (the “Remaining Life”); or (2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields – one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life – and shall interpolate to the Par Call Date of the 2035 Notes to be redeemed on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or (3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the Redemption Date.

If on the third business day preceding the Redemption Date H.15 or any successor designation or publication is no longer published, the Company shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second business day preceding such Redemption Date of the United States Treasury security maturing on, or with a maturity that is closest to, the Par Call Date of the 2035 Notes to be redeemed. If there is no United States Treasury security maturing on the Par Call Date of the 2035 Notes to be redeemed but there are two or more United States Treasury securities with a maturity date equally distant from such Par Call Date of the 2035 Notes to be redeemed, one with a maturity date preceding such Par Call Date of the 2035 Notes to be redeemed and one with a maturity date following such Par Call Date of the 2035 Notes to be redeemed, the Company shall select the United States Treasury security with a maturity date preceding such Par Call Date of the 2035 Notes to be redeemed. If there are two or more United States Treasury securities maturing on the Par Call Date of the 2035 Notes to be redeemed or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Company shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid

and asked prices for such United States Treasury securities at 11:00 a.m., New York City time on such day. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal amount) at 11:00 a.m., New York City time on such day, of such United States Treasury security, and rounded to three decimal places.

The Company’s actions and determinations in determining the Redemption Price shall be conclusive and binding for all purposes, absent manifest error.

In the case of a partial redemption of the 2035 Notes, selection of the 2035 Notes for redemption will be made pro rata, by lot or by such other method as the Trustee in its sole discretion deems appropriate and fair. No 2035 Notes of a principal amount of $2,000 or less will be redeemed in part. If any 2035 Note is to be redeemed in part only, the notice of redemption that relates to the 2035 Note will state the portion of the principal amount of the 2035 Note to be redeemed. A new 2035 Note in a principal amount equal to the unredeemed portion of the 2035 Note will be issued in the name of the Holder of the 2035 Note upon surrender for cancellation of the original 2035 Note. For so long as the 2035 Notes to be redeemed are held by The Depository Trust Company (“DTC”) (or another depositary), the redemption of the 2035 Notes shall be done in accordance with the policies and procedures of the depositary.

Unless the Company defaults in payment of the Redemption Price, on and after the Redemption Date interest will cease to accrue on the 2035 Notes or portions thereof called for redemption.

10. Payment of the principal and interest on the 2035 Notes will be made at the office or agency of the Company maintained for that purpose in New York, New York (initially, the Corporate Trust Office of the Trustee), provided that at the option of the Company payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Security Register.

11. The provisions on defeasance and covenant defeasance in Article Thirteen of the Indenture shall apply to the 2035 Notes.

12. The 2035 Notes shall be issued in the form of one or more Book-Entry Securities and the Depository for such Book-Entry Securities shall be The Depository Trust Company, Clearstream Banking societé anonyme and Euroclear Bank SA/NV.

13. The form of the 2035 Notes attached hereto as Annex A is hereby approved.

Capitalized terms used herein and not otherwise defined herein have the meanings specified in the Indenture.

IN WITNESS WHEREOF, we have hereunto signed our names this ninth day of September, 2025.


			/s/ Melissa Leonard
			Name:			Melissa Leonard
			Title:			Senior Vice President and Treasurer


			/s/ Kelly E. W. Grez
			Name:			Kelly E. W. Grez
			Title:			Corporate Secretary

[Section 301 Officers’ Certificate – 2035 Notes]

Annex A

[FORM OF GLOBAL NOTES]


REGISTERED No. R-[1][2][3][4] CUSIP NO. 58933Y BS3			REGISTERED PRINCIPAL AMOUNT: $[●]1

MERCK & CO., INC.

4.950% NOTES DUE 2035

1 On September 9, 2025, the 2035 Notes will be issued in the form of four Book-Entry Securities in the principal amounts of $500,000,000, $500,000,000, $500,000,000 and $250,000,000.

A-2

Merck & Co., Inc., a New Jersey corporation (hereinafter called the “Company”, which term includes any successor corporation under the Indenture hereinafter referred to), for value received, hereby promises to pay to Cede & Co., as nominee for The Depository Trust Company, or registered assigns, the principal sum of [●] Hundred Million Dollars ($[●]) on September 15, 2035 and to pay interest thereon from and including September 9, 2025 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually in arrears on March 15 and September 15 in each year and at Maturity, commencing on March 15, 2026, at a rate per annum of 4.950%, until the principal hereof is paid or made available for payment, and (to the extent that the payment of such interest shall be legally enforceable) at the interest rate specified above on any overdue principal and premium and on any overdue installment of interest. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be the March 1 or September 1 (whether or not a Business Day in New York City), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Securities of this series may be listed, and upon such notice as may be required by such exchange, all as more fully provided in said Indenture.

A-3

[Signature page follows]

A-4

IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed under its corporate seal.

Dated: September 9, 2025

MERCK & CO., INC.

By:

Name:

Title:


Attest:

By:

Name:
Title:

A-5

CERTIFICATE OF AUTHENTICATION

This is one of the Securities of the series designated herein referred to in the within-mentioned Indenture.


			U.S. BANK TRUST NATIONAL ASSOCIATION,
			As Trustee


			By:
						Authorized Officer

A-6

[REVERSE OF SECURITY]

MERCK & CO., INC.

4.950% NOTES DUE 2035

This Security is one of the series designated on the face hereof. The aggregate principal amount of such series is $1,750,000,000 provided that the Company may increase such aggregate principal amount at any time.

This Security is not subject to any sinking fund.

A-7

(1) (a) the sum of the present values of the remaining scheduled payments of principal and interest on the Securities to be redeemed discounted to the Redemption Date (assuming the Securities matured on the Par Call Date) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 15 basis points less (b) interest accrued to, but excluding, the Redemption Date, and

(2) 100% of the principal amount of the Securities to be redeemed,

plus, in either case, accrued and unpaid interest thereon to, but excluding, the Redemption Date.

On or after June 15, 2035 (three months prior to the Stated Maturity of the Securities, or the “Par Call Date”), the Company may redeem the Securities in whole or in part, at any time and from time to time, at a Redemption Price equal to 100% of the principal amount of the Securities being redeemed plus accrued and unpaid interest thereon to, but excluding, the Redemption Date.

“Treasury Rate” means, with respect to any Redemption Date, as applicable, the yield determined by the Company in accordance with the following two paragraphs.

The Treasury Rate shall be determined by the Company after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the Redemption Date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading). In determining the Treasury Rate, the Company shall select, as applicable: (1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the Redemption Date to the Par Call Date of the Securities to be redeemed (the “Remaining Life”); or (2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields – one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life – and shall interpolate to the Par Call Date of the Securities to be redeemed on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or (3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the Redemption Date.

A-8

If on the third business day preceding the Redemption Date H.15 or any successor designation or publication is no longer published, the Company shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second business day preceding such Redemption Date of the United States Treasury security maturing on, or with a maturity that is closest to, the Par Call Date of the Securities to be redeemed. If there is no United States Treasury security maturing on the Par Call Date of the Securities to be redeemed but there are two or more United States Treasury securities with a maturity date equally distant from such Par Call Date of the Securities to be redeemed, one with a maturity date preceding such Par Call Date of the Securities to be redeemed and one with a maturity date following such Par Call Date of the Securities to be redeemed, the Company shall select the United States Treasury security with a maturity date preceding such Par Call Date of the Securities to be redeemed. If there are two or more United States Treasury securities maturing on the Par Call Date of the Securities to be redeemed or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Company shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time on such day. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal amount) at 11:00 a.m., New York City time on such day, of such United States Treasury security, and rounded to three decimal places.

The Company’s actions and determinations in determining the Redemption Price shall be conclusive and binding for all purposes, absent manifest error.

Unless the Company defaults in payment of the Redemption Price, on and after the Redemption Date interest will cease to accrue on the Securities or portions thereof called for redemption.

A-9

A-10

All terms used in this Security which are defined in the Indenture shall have the meanings assigned to them in the Indenture.

A-11

ABBREVIATIONS

The following abbreviations, when used in the inscription on the face of the within Security, shall be construed as though they were written out in full according to applicable laws or regulations.

TEN COM

as tenants in common

TEN ENT

as tenants by the entireties

JT TEN

as joint tenants with right of survivorship and not as tenants in common

UNIF GIFT MIN ACT -

Custodian

(Cust)

(Minor)

under Uniform Gifts to Minors Act

(State)

Additional abbreviations may also be used
though not in the above list.

A-12

ASSIGNMENT

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto _________________________________________________________________

PLEASE INSERT SOCIAL SECURITY OR OTHER

IDENTIFYING NUMBER OF ASSIGNEE






			(Please Print or Typewrite Name and Address, Including Postal Zip Code, of Assignee)


			the within Security and all rights thereunder, and hereby irrevocably constitutes and
			appoints

to transfer said Security on the books of the Company, with full power of substitution in the premises.

Dated: __________________

Signature Guaranteed

NOTICE: Signature must be guaranteed by a member firm of the New York Stock Exchange or a commercial bank or trust company.

NOTICE: The signature to this assignment must correspond with the name as written upon the face of the within Security in every particular, without alteration or enlargement or any change whatever.

A-13

Exhibit 4.6

5.700% NOTES DUE 2055

MERCK & CO., INC.

Officers’ Certificate

Pursuant to the unanimous written consent and resolutions (collectively, the “Resolutions”) of the Board of Directors of Merck & Co., Inc. (the “Company”) (i) duly adopted and dated March 14, 2024 and (ii) adopted at a meeting duly called and held on November 30, 2021 (at which meeting a quorum was present and acting throughout), which authorized the Company to issue and sell its debt securities and empowered an Authorized Officer (as defined in the Resolutions) to approve the form and terms of such debt securities, Melissa Leonard, Senior Vice President and Treasurer and Kelly E. W. Grez, Corporate Secretary, each hereby approves and establishes under the Indenture, dated as of January 6, 2010 (the “Indenture”), between the Company and U.S. Bank Trust National Association, as Trustee (the “Trustee”), a series of debt securities the terms of which are as follows:

1. The title of the debt securities of such series shall be 5.700% Notes due 2055 (the “2055 Notes”).

2. The aggregate principal amount of the 2055 Notes which may be authenticated and delivered under the Indenture is initially limited to $1,250,000,000, except for 2055 Notes authenticated and delivered upon registration or transfer of, or in exchange for, or in lieu of, other 2055 Notes of the series pursuant to Section 304, 305, 306, 906 or 1107 of the Indenture and except for any 2055 Notes which, pursuant to Section 303 of the Indenture, are deemed never to have been authenticated and delivered under the Indenture.

3. The Company shall have the right from time to time, without the consent of the Holders of the 2055 Notes, to create and issue additional notes with the same terms and conditions as the 2055 Notes except for the issue date, issue price and the first payment of interest thereon (“Additional Notes”), provided that if the Additional Notes are not fungible with the previously outstanding 2055 Notes for U.S. federal income tax purposes, such Additional Notes will have a separate CUSIP. Additional Notes will be consolidated with and will form a single series with the previously outstanding 2055 Notes. Any election by the Company to so increase such aggregate principal amount shall be evidenced by a certificate of an Authorized Officer or Authorized Officers. No Additional Notes may be issued if an Event of Default has occurred or is continuing with respect to the 2055 Notes.

4. The 2055 Notes shall be issued in denominations of $2,000 and integral multiples of $1,000 in excess thereof.

5. The proceeds to the Company (after deducting the underwriting discounts and commissions but before deducting certain expenses payable by the Company in connection with the issuance of the 2055 Notes) shall be 98.899% of the aggregate principal amount of the 2055 Notes.

6. The maturity date on which the principal of each of the 2055 Notes is payable shall be September 15, 2055.

7. The 2055 Notes shall bear interest at the rate of 5.700% per annum from (and including) September 9, 2025. Interest shall be payable on each Interest Payment Date and at the maturity date. Interest payments shall be in the amount of interest accrued to, but excluding, the relevant Interest Payment Date or the maturity date, as applicable.

8. The Interest Payment Dates for the 2055 Notes shall be March 15 and September 15 of each year, commencing on March 15, 2026, and the Regular Record Dates for the 2055 Notes shall be the preceding March 1 or September 1, as the case may be.

If any payment date for the 2055 Notes is not a business day, the Company will make the payment on the next business day, but the Company will not be liable for any additional interest as a result of the delay in payment. With respect to the 2055 Notes, business day means any Monday, Tuesday, Wednesday, Thursday or Friday which is not a day when banking institutions in the place of payment are authorized or obligated by law or executive order to be closed.

9. Prior to the Par Call Date, the Company may redeem the 2055 Notes at its option, in whole or in part, at any time and from time to time, at a Redemption Price (expressed as a percentage of principal amount and rounded to three decimal places) equal to the greater of:

(1) (a) the sum of the present values of the remaining scheduled payments of principal and interest on the 2055 Notes to be redeemed discounted to the Redemption Date (assuming the 2055 Notes matured on the Par Call Date) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 15 basis points less (b) interest accrued to, but excluding, the Redemption Date, and

(2) 100% of the principal amount of the 2055 Notes to be redeemed,

plus, in either case, accrued and unpaid interest thereon to, but excluding, the Redemption Date.

On or after the Par Call Date, the Company may redeem the 2055 Notes in whole or in part, at any time and from time to time, at a Redemption Price equal to 100% of the principal amount of the 2055 Notes being redeemed plus accrued and unpaid interest thereon to, but excluding, the Redemption Date.

“Par Call Date” means March 15, 2055, the date that is six months prior to the maturity of the 2055 Notes.

“Treasury Rate” means, with respect to any Redemption Date, as applicable, the yield determined by the Company in accordance with the following two paragraphs.

The Treasury Rate shall be determined by the Company after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the Redemption Date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading). In determining the Treasury Rate, the Company shall select, as applicable: (1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the Redemption Date to the Par Call Date of the 2055 Notes to be redeemed (the “Remaining Life”); or (2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields – one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life – and shall interpolate to the Par Call Date of the 2055 Notes to be redeemed on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or (3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the Redemption Date.

If on the third business day preceding the Redemption Date H.15 or any successor designation or publication is no longer published, the Company shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second business day preceding such Redemption Date of the United States Treasury security maturing on, or with a maturity that is closest to, the Par Call Date of the 2055 Notes to be redeemed. If there is no United States Treasury security maturing on the Par Call Date of the 2055 Notes to be redeemed but there are two or more United States Treasury securities with a maturity date equally distant from such Par Call Date of the 2055 Notes to be redeemed, one with a maturity date preceding such Par Call Date of the 2055 Notes to be redeemed and one with a maturity date following such Par Call Date of the 2055 Notes to be redeemed, the Company shall select the United States Treasury security with a maturity date preceding such Par Call Date of the 2055 Notes to be redeemed. If there are two or more United States Treasury securities maturing on the Par Call Date of the 2055 Notes to be redeemed or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Company shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time on such day. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal

amount) at 11:00 a.m., New York City time on such day, of such United States Treasury security, and rounded to three decimal places.

The Company’s actions and determinations in determining the Redemption Price shall be conclusive and binding for all purposes, absent manifest error.

In the case of a partial redemption of the 2055 Notes, selection of the 2055 Notes for redemption will be made pro rata, by lot or by such other method as the Trustee in its sole discretion deems appropriate and fair. No 2055 Notes of a principal amount of $2,000 or less will be redeemed in part. If any 2055 Note is to be redeemed in part only, the notice of redemption that relates to the 2055 Note will state the portion of the principal amount of the 2055 Note to be redeemed. A new 2055 Note in a principal amount equal to the unredeemed portion of the 2055 Note will be issued in the name of the Holder of the 2055 Note upon surrender for cancellation of the original 2055 Note. For so long as the 2055 Notes to be redeemed are held by The Depository Trust Company (“DTC”) (or another depositary), the redemption of the 2055 Notes shall be done in accordance with the policies and procedures of the depositary.

Unless the Company defaults in payment of the Redemption Price, on and after the Redemption Date interest will cease to accrue on the 2055 Notes or portions thereof called for redemption.

10. Payment of the principal and interest on the 2055 Notes will be made at the office or agency of the Company maintained for that purpose in New York, New York (initially, the Corporate Trust Office of the Trustee), provided that at the option of the Company payment of interest may be made by check mailed to the address of the Person entitled thereto as such address shall appear in the Security Register.

11. The provisions on defeasance and covenant defeasance in Article Thirteen of the Indenture shall apply to the 2055 Notes.

12. The 2055 Notes shall be issued in the form of one or more Book-Entry Securities and the Depository for such Book-Entry Securities shall be The Depository Trust Company, Clearstream Banking societé anonyme and Euroclear Bank SA/NV.

13. The form of the 2055 Notes attached hereto as Annex A is hereby approved.

Capitalized terms used herein and not otherwise defined herein have the meanings specified in the Indenture.

IN WITNESS WHEREOF, we have hereunto signed our names this ninth day of September, 2025.


			/s/ Melissa Leonard
			Name:			Melissa Leonard
			Title:			Senior Vice President and Treasurer


			/s/ Kelly E. W. Grez
			Name:			Kelly E. W. Grez
			Title:			Corporate Secretary

[Section 301 Officers’ Certificate – 2055 Notes]

Annex A

[FORM OF GLOBAL NOTES]


REGISTERED			REGISTERED
No. R-[1][2][3]			PRINCIPAL AMOUNT: $[●]1
CUSIP NO. 58933Y BT1

MERCK & CO., INC.

5.700% NOTES DUE 2055

1 On September 9, 2025, the 2055 Notes will be issued in the form of three Book-Entry Securities in the principal amounts of $500,000,000, $500,000,000 and $250,000,000.

A-2

Merck & Co., Inc., a New Jersey corporation (hereinafter called the “Company”, which term includes any successor corporation under the Indenture hereinafter referred to), for value received, hereby promises to pay to Cede & Co., as nominee for The Depository Trust Company, or registered assigns, the principal sum of [●] Hundred Million Dollars ($[●]) on September 15, 2055 and to pay interest thereon from and including September 9, 2025 or from the most recent Interest Payment Date to which interest has been paid or duly provided for, semi-annually in arrears on March 15 and September 15 in each year and at Maturity, commencing on March 15, 2026, at a rate per annum of 5.700%, until the principal hereof is paid or made available for payment, and (to the extent that the payment of such interest shall be legally enforceable) at the interest rate specified above on any overdue principal and premium and on any overdue installment of interest. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in such Indenture, be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on the Regular Record Date for such interest, which shall be the March 1 or September 1 (whether or not a Business Day in New York City), as the case may be, next preceding such Interest Payment Date. Any such interest not so punctually paid or duly provided for will forthwith cease to be payable to the Holder on such Regular Record Date and may either be paid to the Person in whose name this Security (or one or more Predecessor Securities) is registered at the close of business on a Special Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Securities of this series not less than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Securities of this series may be listed, and upon such notice as may be required by such exchange, all as more fully provided in said Indenture.

A-3

[Signature page follows]

A-4

IN WITNESS WHEREOF, the Company has caused this instrument to be duly executed under its corporate seal.

Dated: September 9, 2025

MERCK & CO., INC.

By:

Name:

Title:


Attest:

By:

Name:
Title:

A-5

CERTIFICATE OF AUTHENTICATION

This is one of the Securities of the series designated herein referred to in the within-mentioned Indenture.


			U.S. BANK TRUST NATIONAL ASSOCIATION,
			As Trustee


			By:
						Authorized Officer

A-6

[REVERSE OF SECURITY]

MERCK & CO., INC.

5.700% NOTES DUE 2055

This Security is one of the series designated on the face hereof. The aggregate principal amount of such series is $1,250,000,000 provided that the Company may increase such aggregate principal amount at any time.

This Security is not subject to any sinking fund.

A-7

(1) (a) the sum of the present values of the remaining scheduled payments of principal and interest on the Securities to be redeemed discounted to the Redemption Date (assuming the Securities matured on the Par Call Date) on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 15 basis points less (b) interest accrued to, but excluding, the Redemption Date, and

(2) 100% of the principal amount of the Securities to be redeemed,

plus, in either case, accrued and unpaid interest thereon to, but excluding, the Redemption Date.

On or after March 15, 2055 (six months prior to the Stated Maturity of the Securities, or the “Par Call Date”), the Company may redeem the Securities in whole or in part, at any time and from time to time, at a Redemption Price equal to 100% of the principal amount of the Securities being redeemed plus accrued and unpaid interest thereon to, but excluding, the Redemption Date.

“Treasury Rate” means, with respect to any Redemption Date, as applicable, the yield determined by the Company in accordance with the following two paragraphs.

The Treasury Rate shall be determined by the Company after 4:15 p.m., New York City time (or after such time as yields on U.S. government securities are posted daily by the Board of Governors of the Federal Reserve System), on the third business day preceding the Redemption Date based upon the yield or yields for the most recent day that appear after such time on such day in the most recent statistical release published by the Board of Governors of the Federal Reserve System designated as “Selected Interest Rates (Daily)—H.15” (or any successor designation or publication) (“H.15”) under the caption “U.S. government securities–Treasury constant maturities–Nominal” (or any successor caption or heading). In determining the Treasury Rate, the Company shall select, as applicable: (1) the yield for the Treasury constant maturity on H.15 exactly equal to the period from the Redemption Date to the Par Call Date of the Securities to be redeemed (the “Remaining Life”); or (2) if there is no such Treasury constant maturity on H.15 exactly equal to the Remaining Life, the two yields – one yield corresponding to the Treasury constant maturity on H.15 immediately shorter than and one yield corresponding to the Treasury constant maturity on H.15 immediately longer than the Remaining Life – and shall interpolate to the Par Call Date of the Securities to be redeemed on a straight-line basis (using the actual number of days) using such yields and rounding the result to three decimal places; or (3) if there is no such Treasury constant maturity on H.15 shorter than or longer than the Remaining Life, the yield for the single Treasury constant maturity on H.15 closest to the Remaining Life. For purposes of this paragraph, the applicable Treasury constant maturity or maturities on H.15 shall be deemed to have a maturity date equal to the relevant number of months or years, as applicable, of such Treasury constant maturity from the Redemption Date.

A-8

If on the third business day preceding the Redemption Date H.15 or any successor designation or publication is no longer published, the Company shall calculate the Treasury Rate based on the rate per annum equal to the semi-annual equivalent yield to maturity at 11:00 a.m., New York City time, on the second business day preceding such Redemption Date of the United States Treasury security maturing on, or with a maturity that is closest to, the Par Call Date of the Securities to be redeemed. If there is no United States Treasury security maturing on the Par Call Date of the Securities to be redeemed but there are two or more United States Treasury securities with a maturity date equally distant from such Par Call Date of the Securities to be redeemed, one with a maturity date preceding such Par Call Date of the Securities to be redeemed and one with a maturity date following such Par Call Date of the Securities to be redeemed, the Company shall select the United States Treasury security with a maturity date preceding such Par Call Date of the Securities to be redeemed. If there are two or more United States Treasury securities maturing on the Par Call Date of the Securities to be redeemed or two or more United States Treasury securities meeting the criteria of the preceding sentence, the Company shall select from among these two or more United States Treasury securities the United States Treasury security that is trading closest to par based upon the average of the bid and asked prices for such United States Treasury securities at 11:00 a.m., New York City time on such day. In determining the Treasury Rate in accordance with the terms of this paragraph, the semi-annual yield to maturity of the applicable United States Treasury security shall be based upon the average of the bid and asked prices (expressed as a percentage of principal amount) at 11:00 a.m., New York City time on such day, of such United States Treasury security, and rounded to three decimal places.

The Company’s actions and determinations in determining the Redemption Price shall be conclusive and binding for all purposes, absent manifest error.

Unless the Company defaults in payment of the Redemption Price, on and after the Redemption Date interest will cease to accrue on the Securities or portions thereof called for redemption.

A-9

A-10

All terms used in this Security which are defined in the Indenture shall have the meanings assigned to them in the Indenture.

A-11

ABBREVIATIONS

The following abbreviations, when used in the inscription on the face of the within Security, shall be construed as though they were written out in full according to applicable laws or regulations.

TEN COM

as tenants in common

TEN ENT

as tenants by the entireties

JT TEN

as joint tenants with right of survivorship and not as tenants in common

UNIF GIFT MIN ACT -

Custodian

(Cust)

(Minor)

under Uniform Gifts to Minors Act

(State)

Additional abbreviations may also be used
though not in the above list.

A-12

ASSIGNMENT

FOR VALUE RECEIVED, the undersigned hereby sell(s), assign(s) and transfer(s) unto _________________________________________________________________

PLEASE INSERT SOCIAL SECURITY OR OTHER

IDENTIFYING NUMBER OF ASSIGNEE





			(Please Print or Typewrite Name and Address, Including Postal Zip Code, of Assignee)


			the within Security and all rights thereunder, and hereby irrevocably constitutes and
			appoints

to transfer said Security on the books of the Company, with full power of substitution in the premises.

Dated: __________________

Signature Guaranteed

NOTICE: Signature must be guaranteed by a member firm of the New York Stock Exchange or a commercial bank or trust company.

NOTICE: The signature to this assignment must correspond with the name as written upon the face of the within Security in every particular, without alteration or enlargement or any change whatever.

A-13

Exhibit 5.1

[Letterhead of Merck & Co., Inc.]

September 9, 2025

Merck & Co., Inc.

126 East Lincoln Avenue

Rahway, New Jersey 07065

Re: Merck & Co., Inc. — $500,000,000 Floating Rate Notes due 2027

$750,000,000 3.850% Notes due 2027

$750,000,000 4.150% Notes due 2030

$1,000,000,000 4.550% Notes due 2032

$1,750,000,000 4.950% Notes due 2035

$1,250,000,000 5.700% Notes due 2055

Ladies and Gentlemen:

I am the Executive Vice President and General Counsel of Merck & Co., Inc., a New Jersey corporation (the “Company”), and in such capacity have acted as counsel for the Company in connection with the issuance of the Company’s (i) $500,000,000 Floating Rate Notes due 2027, (ii) $750,000,000 3.850% Notes due 2027, (iii) $750,000,000 4.150% Notes due 2030, (iv) $1,000,000,000 4.550% Notes due 2032, (v) $1,750,000,000 4.950% Notes due 2035 and (vi) $1,250,000,000 5.700% Notes due 2055 (collectively, the “Securities”). I, or attorneys under my general supervision, have examined such corporate records, certificates and other documents, including the Registration Statement on Form S-3ASR (the “Initial Registration Statement”) filed on March 19, 2024, as amended by Post-Effective Amendment No. 1 (the “Post-Effective Amendment” and, together with the Initial Registration Statement as amended by the Post-Effective Amendment, the “Registration Statement”) filed on May 14, 2024 relating to the Securities, and have reviewed such questions of law as I have considered necessary or appropriate for the purposes of this opinion.

I am admitted to practice law in California, New Jersey and the District of Columbia. The opinions expressed herein are limited in all respects to the federal laws of the United States of America, the laws of the State of New York, and the New Jersey Business Corporation Act.

As used herein, “Indenture” means the indenture, dated as of January 6, 2010, between the Company and U.S. Bank Trust National Association, as trustee.

Upon the basis of the foregoing examination and review, I advise you that, in my opinion:

1. The Company is a corporation duly organized and existing under the laws of the State of New Jersey.

2. The Securities have been duly authorized and the global securities representing the Securities have been duly executed, and assuming the Securities have been duly authenticated and delivered in accordance with the Indenture relating to the Securities and receipt by the Company of payment of the issue price of the Securities, will be legally issued and will constitute valid and binding obligations of the Company, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and similar laws of general applicability relating to or affecting creditors’ rights and to general equity principles.

I hereby consent to the filing of this opinion as an exhibit to the Registration Statement and to the reference to me under the heading “Validity of Debt Securities” in the Prospectus and “Validity of the Notes” in the Prospectus Supplement. In giving this consent, I do not thereby admit that I am in the category of persons whose consent is required under Section 7 of the Securities Act of 1933, as amended.


			Very truly yours,


			/s/ Jennifer Zachary
			Jennifer Zachary
			Executive Vice President and General Counsel