Exhibit 32.1

CERTIFICATIONS OF PRINCIPAL EXECUTIVE OFFICER

PURSUANT TO 18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO SECTION 906

OF THE SARBANES-OXLEY ACT OF 2002

The undersigned officer of Amphastar Pharmaceuticals, Inc. (the “Company”), hereby certifies, to the best of such officer’s knowledge, that:

(i) the Annual Report on Form 10-K of the Company for the year ended December 31, 2023 (the “Report”) fully complies with the requirements of Section 13(a) or Section 15(d) of the Securities Exchange Act of 1934 and

(ii) the information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company at the dates and for the periods indicated.

Date: February 29, 2024	By:	/s/ JACK Y. ZHANG
		Jack Y. Zhang
		Chief Executive Officer
		(Principal Executive Officer)