Exhibit 5.1

Simpson Thacher & Bartlett LLP

425 LEXINGTON AVENUE

NEW YORK, NY 10017-3954

TELEPHONE: +1-212-455-2000

FACSIMILE: +1-212-455-2502

Direct Dial Number E-mail Address

March 2, 2023

Amneal Pharmaceuticals, Inc.

400 Crossing Blvd

Bridgewater, New Jersey 08807

Ladies and Gentlemen:

We have acted as counsel to Amneal Pharmaceuticals, Inc., a Delaware corporation (the “Company”), in connection with the Registration Statement on Form S-3 (the “Registration Statement”) filed by the Company with the Securities and Exchange Commission under the Securities Act of 1933, as amended (the “Securities Act”), relating to the issuance and sale by the Company of (i) shares of Class A common stock, par value $0.01 per share, of the Company (the “Common Stock”); (ii) shares of preferred stock, par value $0.01 per share, of the Company (the “Preferred Stock”); and (iii) debt securities of the Company, which may be either senior debt securities or subordinated debt securities (collectively, the “Debt Securities”). The Common Stock, the Preferred Stock and the Debt Securities are hereinafter referred to collectively as the “Securities.” The Securities may be issued and sold or delivered from time to time for an aggregate initial offering price not to exceed $1,250,000,000 as set forth in the Registration Statement, any amendment thereto, the prospectus contained therein (the “Prospectus”) and supplements to the Prospectus and pursuant to Rule 415 under the Securities Act.

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The Debt Securities will be issued under an Indenture (the “Indenture”), between the Company and such trustee as shall be named therein.

We have examined the Registration Statement and the form of the Indenture, which is an exhibit to the Registration Statement. In addition, we have examined, and have relied as to matters of fact upon, originals, or duplicates or certified or conformed copies, of such records, agreements, documents and other instruments and such certificates or comparable documents of public officials and of officers and representatives of the Company and have made such other investigations as we have deemed relevant and necessary in connection with the opinions hereinafter set forth.

In rendering the opinions set forth below, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as duplicates or certified or conformed copies, and the authenticity of the originals of such latter documents.

In rendering the opinions set forth below, we have assumed further that, at the time of execution, authentication, issuance and delivery, as applicable, of the Indenture and any Debt Securities, (1) the Company will be validly existing and in good standing under the law of the jurisdiction in which it is organized and the Indenture will have been duly authorized, executed and delivered by the Company in accordance with its organizational documents and the law of the jurisdiction in which it is organized, (2) the execution, issuance, delivery and performance, as applicable, by the Company of the Debt Securities and the Indenture will not constitute a breach or violation of its organizational documents or violate the law of the jurisdiction in which it is organized or any other jurisdiction (except that no such assumption

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is made with respect to the law of the State of New York or the Delaware General Corporation Law) and (3) the execution, issuance, delivery and performance, as applicable, by the Company of the Debt Securities and the Indenture (a) will not constitute a breach or default under any agreement or instrument which is binding upon the Company and (b) will comply with all applicable regulatory requirements. We have assumed further that, at the time of execution, authentication, issuance and delivery of any Debt Securities, the Indenture will be the valid and legally binding obligation of all parties thereto other than the Company. We also have assumed that, with respect to the issuance of any shares of Common Stock or Preferred Stock, the amount of valid consideration paid in respect of such shares will equal or exceed the par value of such shares.

Based upon the foregoing, and subject to the qualifications, assumptions and limitations stated herein, we are of the opinion that:

1. With respect to the Common Stock, assuming (a) the taking by the Board of Directors of the Company or a duly constituted and acting committee of such Board of Directors (such Board of Directors or committee being referred to herein as the “Board”) of all necessary corporate action to authorize and approve the issuance of the Common Stock and the terms of the offering thereof so as not to violate any applicable law or agreement or instrument then binding on the Company and (b) due issuance and delivery of the Common Stock from the Company’s authorized but unissued Common Stock, upon payment therefor in accordance with the applicable definitive purchase, underwriting or similar agreement approved by the Board and otherwise in accordance with the provisions of such agreement and the charter and bylaws of the Company, the Common Stock will be validly issued, fully paid and nonassessable.

2. With respect to the Preferred Stock, assuming (a) the taking of all necessary corporate action to authorize and approve the issuance and terms of the Preferred Stock and the terms of the offering thereof so as not to violate any applicable law or agreement or instrument then binding on the Company, (b) due filing of the applicable definitive Certificate of Designations with respect to such Preferred Stock and (c) due issuance and delivery of the Preferred Stock, upon payment therefor in accordance with the applicable definitive underwriting, purchase or similar agreement approved by the Board of Directors of the Company and otherwise in accordance with the provisions of such agreement, the charter and bylaws and the Delaware General Corporation Law, the Preferred Stock will be validly issued, fully paid and nonassessable.

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3. With respect to the Debt Securities, assuming (a) the taking of all necessary corporate action to approve the issuance and terms of the Debt Securities, the terms of the offering thereof, the execution and delivery of the Indenture and related matters by the Board or, unless the Debt Securities are convertible into equity securities of the Company, duly authorized officers of the Company so as not to violate any applicable law or agreement or instrument then binding on the Company and (b) the due execution, authentication, issuance and delivery of such Debt Securities, upon payment of the consideration therefor provided for in the applicable definitive purchase, underwriting or similar agreement approved by the Board or, unless the Debt Securities are convertible into equity securities of the Company, duly authorized officers of the Company and otherwise in accordance with the provisions of the Indenture and such agreement, such Debt Securities will constitute valid and legally binding obligations of the Company enforceable against the Company in accordance with their terms.

Our opinion set forth in paragraph 3 above is subject to (i) the effects of bankruptcy, insolvency, fraudulent conveyance, reorganization, moratorium and other similar laws relating to or affecting creditors’ rights generally, (ii) general equitable principles (whether considered in a proceeding in equity or at law) and (iii) an implied covenant of good faith and fair dealing. In addition, we express no opinion as to the validity, legally binding effect or enforceability of (A) the waiver of rights and defenses contained in Section 4.4 of the Indenture or (B) Section 10.13 of the Indenture relating to the severability of provisions of the Indenture.

In connection with the provisions of the Indenture whereby the parties submit to the jurisdiction of the courts of the United States of America located in the City of New York, we note the limitations of 28 U.S.C. Sections 1331 and 1332 on subject matter jurisdiction of the federal courts. In connection with the provisions of the Indenture that relate to forum selection (including, without limitation, any waiver of any objection to venue or any objection that a court is an inconvenient forum), we note that under N.Y.C.P.L.R. Section 510 a New York State court may have discretion to transfer the place of trial, and under 28 U.S.C. Section 1404(a) a United States District Court has discretion to transfer an action from one federal court to another.

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We do not express any opinion herein concerning any law other than the law of the State of New York and the Delaware General Corporation Law.

We hereby consent to the filing of this opinion letter as Exhibit 5.1 to the Registration Statement and to the use of our name under the caption “Legal Matters” in the Prospectus included in the Registration Statement.

Very truly yours,

/s/ SIMPSON THACHER & BARTLETT LLP

SIMPSON THACHER & BARTLETT LLP