Filed Pursuant to Rule 424(b)(3)
Registration No. 333-107820

AVANIR PHARMACEUTICALS

SUPPLEMENT NO. 1 TO PROSPECTUS DATED AUGUST 19, 2003

     This supplement, dated April 6, 2004, supplements certain information contained in our prospectus, dated August 19, 2003 (the “Prospectus”). This supplement is not complete without, and may not be delivered or utilized except in connection with, the Prospectus, including any amendments or supplements thereto.

     The information contained in the table under the caption “Selling Security Holders” on page 8 of the Prospectus is hereby supplemented by: (i) adding to the table the selling security holder set forth below under Schedule 1, and (ii) restating the holdings of the selling security holder set forth below under Schedule 2.

Schedule 1

Schedule 2

     Information concerning the selling security holders is based upon information provided to us by the security holders. This information may change from time to time and any changed information will be set forth in future prospectus supplements, if and when necessary. Additionally, the selling security holders identified above and in the Prospectus may have sold, transferred or otherwise disposed of all or a portion of their Class A common stock since the date on which they last provided the Company with information about their holdings.