默沙东美股招股说明书(2026-05-18版)

Merck & Co., Inc., Rahway, N.J., USA % Notes due 20% Notes due 20% Notes due 20% Notes due 20% Notes due 20% Notes due 20 aggregate principal amount of ourFloating Rate Notes due 20(the “floating rate notes”), $aggregate principal amount of our% Notesnotes”), $aggregate principal amount of our% Notes due 20(the “20notes”), $aggregate principal amount of our% Notes dueaggregate principal amount of our% Notes due 20(the “20notes”), $aggregate principal amount of our% Notes due 20aggregate principal amount of our% Notes due 20(the “20notes”). We refer to the 20notes, the 20notes, the 20notes, the 20 notes, the 20notes and the 20notes collectively as the “fixed rate notes.” We refer to the fixed rate notes and the floating rate notes collectively as the “notes.” Interest on the floating rate notes is payable on,,andof each year, beginning on, 2026, and interest on the fixed rate notes is payable onandof each year, beginning on, 2026. The floating rate notes will bear interest at a floating rate equal to Compounded SOFR (as defined herein) plus%, subject tothe provisions set forth under “Description of the Notes—Interest—Floating Rate Notes.” The fixed rate notes of each series will bear interest at the annual interest rate shown above for suchseries of notes. The floating rate notes will mature on, 20, the 20notes will mature on, 20, the 20notes will mature on, 20, the 20notes will mature We may redeem some or all of the fixed rate notes of each series at any time at the applicable redemption price set forth in this prospectus supplement under the caption “Description ofthe Notes—Optional Redemption.” The floating rate notes are not redeemable prior to maturity. On March 25, 2026, we announced a definitive agreement (the “Merger Agreement”) to acquire Terns Pharmaceuticals, Inc. (“Terns”) through a subsidiary (the “Terns Acquisition”). TheTerns Acquisition closed on May 5, 2026. In connection with the closing of the Terns Acquisition, we borrowed funds under a 364-Day Delayed Draw Term Loan Credit Agreement, dated as ofApril 1, 2026 (the “Credit Agreement”), to finance a portion of the consideration for the Terns Acquisition and related fees and expenses. We intend to use the net proceeds of this offering to The notes will be our unsecured senior debt obligations and will rank equally with all of our other unsecured senior indebtedness from time to time outstanding. The notes will be issuedonly in denominations of $2,000 and integral multiples of $1,000 in excess thereof. The notes will not be convertible or exchangeable. Investing in the notes involves risks. See “Risk Factors” beginning on pageS-3of this prospectus supplement and in the documents incorporated by reference in this prospectussupplement and the accompanying prospectus. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securitiesor determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense. Per floating rate noteTotalPer 20noteTotal (1)Plus accrued interest from, 2026, if settlement occurs after that date.Interest on the notes will accrue from, 2026. The notes will not be listed on any securities exchange or automated dealer quotation system. Currently, there is no public market for Citigroup J.P. Morgan TABLE OF CONTENTS Prospectus Supplement About This Prospectus SupplementMerck & Co., Inc., Rahway, N.J., USARisk FactorsForward-Looking StatementsUse of ProceedsCapitalizationDescription of the NotesCertain U.S. Federal Tax ConsequencesUnderwriting(Conflicts of Interest)Incorporation of Certain Documents by ReferenceValidity of the NotesExperts Prospectus About This ProspectusMerck & Co., Inc., Rahway, N.J., USAMSD Netherlands Capital B.V.Risk FactorsForward-Looking StatementsUse of ProceedsDescription of Debt Securities Parent May OfferDescription of Debt Securities MSD Netherlands May OfferLegal Ownership and Book-Entry IssuancePlan of DistributionValidity of Debt SecuritiesExpertsWhere You Can Find More InformationIncorporation of Certain Documents by ReferenceEnforcement of Judgments ABOUT THIS PROSPECTUS SUPPLEMENT We have not, and the underwriters have not, authorized anyone to provide you with any information other than thatcontained or incorporated by reference in this prospectus supplement, any related free writing prospectus prepared by us orthe accompanying prospectus. We take no responsibility for, and can provide no assurance as to the reliability of any otherinformation that others may give you. If the information varies between this prospectus supplement and the accompanyingprospectus, the information in this prospectus supplement supersedes the information in the accompanying prospectus. We arenot making an offer of these securities in any jurisdiction where the offer or sale is not permitted. Neither the delivery of this MERCK & CO., INC., RAHWAY,