UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of the

Securities Exchange Act of 1934

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☐ Preliminary Proxy Statement

☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

☐ Definitive Proxy Statement

☒ Definitive Additional Materials

☐ Soliciting Material Pursuant to Section 240.14a-12

Merck & Co., Inc.

(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)

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☐ Fee paid previously with preliminary materials.

☐ Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11

Your Vote Counts! MERCK & CO., INC. 2024 Annual Meeting Vote by May 27, 2024 11:59 PM ET MERCK & CO., INC. 126 EAST LINCOLN AVENUE RAHWAY, NJ 07065 V37885-P05716-Z86974 You invested in MERCK & CO., INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy materials for the shareholder meeting to be held on May 28, 2024. Get informed before you vote View the Notice and Proxy Statement and Annual Report on Form 10-K online OR you can receive a free paper or email copy of the material(s) by requesting prior to May 14, 2024. If you would like to request a copy of the material(s) for this and/or future shareholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to sendmaterial@proxyvote.com. If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy. For complete information and to vote, visit www.ProxyVote.com Control # Smartphone users Point your camera here and vote without entering a control number Vote Virtually at the Meeting* May 28, 2024 9:00 a.m. Eastern Time Virtually at: www.virtualshareholdermeeting.com/MRK2024 *Please check the meeting materials for any special requirements for meeting attendance.

Vote at www.ProxyVote.com THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming shareholder meeting. Please follow the instructions on the reverse side to vote these important matters. Board Recommends Voting Items 1. Election of Directors Nominees: 1a. Douglas M. Baker, Jr. For 1b. Mary Ellen Coe For 1c. Pamela J. Craig For 1d. Robert M. Davis For 1e. Thomas H. Glocer For 1f. Risa J. Lavizzo-Mourey, M.D. For 1g. Stephen L. Mayo, Ph.D. For 1h. Paul B. Rothman, M.D. For 1i. Patricia F. Russo For 1j. Christine E. Seidman, M.D. For 1k. Inge G. Thulin For 1l. Kathy J. Warden For 2. Non-binding advisory vote to approve the compensation of our named executive officers. For 3. Ratification of the appointment of the Company’s independent registered public accounting firm for 2024. For 4. Shareholder proposal regarding a shareholder right to act by written consent. Against 5. Shareholder proposal regarding a government censorship transparency report. Against 6. Shareholder proposal regarding a report on respecting workforce civil liberties. Against Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Delivery Settings”. V37886-P05716-Z86974