Exhibit 5.1

	Palo Alto, California 94304-1050 : 650.493.9300f: 650.493.6811
	Wilson Sonsini Goodrich & RosatiProfessional Corporation 650 Page Mill RoadPalo Alto, California 94304-1050 o: 650.493.9300f: 650.493.6811

February 29, 2024

Amphastar Pharmaceuticals, Inc.

11570 6th Street

Rancho Cucamonga, California 91730

Re: Registration Statement on Form S-8

Ladies and Gentlemen:

We have examined the Registration Statement on Form S-8 (the “Registration Statement”) to be filed by Amphastar Pharmaceuticals, Inc., a Delaware corporation, with the Securities and Exchange Commission on or about the date hereof, in connection with the registration under the Securities Act of 1933, as amended, of 1,201,722 shares of common stock, par value $0.0001 per share (the “Shares”) reserved for issuance pursuant to the Amended and Restated 2015 Equity Incentive Plan (the “Plan”).  As your legal counsel, we have reviewed the actions proposed to be taken by you in connection with the issuance and sale of the Shares to be issued under the Plan.

On the basis of the foregoing, and in reliance thereon, we are of the opinion that the Shares, when issued and sold in the manner referred to in the Plan and pursuant to the agreements which accompany the Plan, will be legally and validly issued, fully paid and nonassessable.

We consent to the use of this opinion as an exhibit to the Registration Statement, and further consent to the use of our name wherever appearing in the Registration Statement and any amendments thereto.

Sincerely,

WILSON SONSINI GOODRICH & ROSATI

Professional Corporation

/s/ Wilson Sonsini Goodrich & Rosati, P.C.

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