Exhibit 99.1

JOINT FILING AGREEMENT

The undersigned hereby agree that the Statement on Schedule 13G dated August 26, 2009 with respect to the shares of Common Stock of Ligand Pharmaceuticals Incorporated and any further amendments thereto executed by each and any of the undersigned shall be filed on behalf of each of the undersigned pursuant to and in accordance with the provisions of Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended.

Dated: August 26, 2009

BIOTECHNOLOGY VALUE FUND, L.P.		INVESTMENT 10, L.L.C.
By:	BVF Partners L.P., its general partner	By:	BVF Partners L.P., its investment manager
By:	BVF Inc., its general partner	By:	BVF Inc., its general partner
By:	/s/ Mark N. Lampert	By:	/s/ Mark N. Lampert
	Mark N. Lampert		Mark N. Lampert
	President		President

BIOTECHNOLOGY VALUE FUND II, L.P.		BVF PARTNERS L.P.
By:	BVF Partners L.P., its general partner	By:	BVF Inc., its general partner
By:	BVF Inc., its general partner	By:	/s/ Mark N. Lampert
			Mark N. Lampert
By:	/s/ Mark N. Lampert		President
	Mark N. Lampert
	President

		BVF INC.
BVF INVESTMENTS, L.L.C.
		By:	/s/ Mark N. Lampert
By:	BVF Partners L.P., its manager		Mark N. Lampert
			President
By:	BVF Inc., its general partner
By:	/s/ Mark N. Lampert	/s/ Mark N. Lampert
	Mark N. Lampert	MARK N. LAMPERT
	President