Exhibit A JOINT FILING AGREEMENTA Joint Filing Agreement • December 4th, 2008 • Biotechnology Value Fund L P • Investment advice
Contract Type FiledDecember 4th, 2008 Company IndustryThe undersigned agree that this Amendment No. 2 to Schedule 13G, dated December 4, 2008, relating to the Common Stock of NBIX shall be filed on behalf of the undersigned.