Exhibit 32.1 CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350 AS ADOPTED PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002 Pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, with respect to the Quarterly Report of the Company on Form 10-Q for the quarter ended June 30, 2003 (the "Report"), each of the undersigned officers of Impax Laboratories, Inc. does hereby certify that: 1. The Report fully complies with the requirements of the Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and 2. The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company. Charles Hsiao, Ph.D. Chairman and Co-Chief Executive Officer Date: August 8, 2003 - --------------------------- Charles Hsiao, Ph.D. Barry R. Edwards Co-Chief Executive Officer Date: August 8, 2003 - --------------------------- Barry R. Edwards Cornel C. Spiegler Chief Financial Officer Date: August 8, 2003 - --------------------------- Cornel C. Spiegler The foregoing certification is being furnished solely pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 (Section 1350 of Chapter 63 of Title 18 of the U.S. Code) and is not being filed as part of the Report or as a separate disclosure document. 29