EXHIBIT 99.1

                CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

This certification is intended to accompany the Annual Report of Impax
Laboratories, Inc. (the "Company") on Form 10-K for the period ended December
31, 2002, as filed with the Securities and Exchange Commission on the date
hereof (the "Report"), and is given solely for the purpose of satisfying the
requirements of 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of
the Sarbanes-Oxley Act of 2002. The undersigned, in my capacity as set forth
below, hereby certifies that, to the best of my knowledge:

         1.       The Report fully complies with the requirements of 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.

                                         /s/  CHARLES HSIAO, Ph.D.
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                                             Charles Hsiao, Ph.D.
                                    Chairman and Co-Chief Executive Officer

                                                 March 27, 2003
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