KYTHERA BIOPHARMACEUTICALS, INC. AMENDMENT NO. 1 TO THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

Exhibit 10.1(b)

KYTHERA BIOPHARMACEUTICALS, INC.

AMENDMENT NO. 1 TO

THIRD AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

THIS AMENDMENT NO. 1 is made as of January 27, 2012, between KYTHERA BIOPHARMACEUTICALS, INC., a Delaware corporation (the “Company”), and the Investors set forth on the signature pages hereto.

The Company and the Investors are parties to that certain Third Amended and Restated Investor Rights Agreement, dated as of August 30, 2011 (the “Investors’ Agreement”).  In connection with working capital credit facility with Lighthouse Capital Partners VI, L.P. (“Lighthouse”), the Company issued a warrant to Lighthouse (the “Warrant”) to acquire shares of the Company’s Series D Preferred Stock (the “Preferred Stock”).

As a covenant of the Warrant, the Company agreed to grant Lighthouse registration rights with respect to the shares of the Company’s Common Stock issuable upon conversion of the Preferred Stock, and the Investors, constituting the holders of at least sixty percent (60%) of the Registrable Securities (as defined in the Investors’ Agreement), desire to amend the Investors’ Agreement to include Lighthouse thereunder.

NOW, THEREFORE, in consideration of the mutual covenants contained herein and other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties hereto agree as follows:

1.                                      The definition of “Series D Preferred Stock” set forth in Section 1.1(cc) of the Investor’s Agreement shall be amended in its entirety as follows:

“Series D Preferred Stock” shall mean the shares of Series D Preferred Stock of the Company issued pursuant to the Purchase Agreement and the shares of Series D Preferred Stock of the Company issued or issuable pursuant to that certain Preferred Stock Purchase Warrant, dated December 30, 2011, issued to Lighthouse Capital Partners VI, L.P. by the Company.”

2.                                      Exhibit A to the Investors’ Agreement shall be amended in its entirety as set forth in Attachment 1 hereto to include Lighthouse Capital Partners VI, L.P. as an Investor under the Investors’ Agreement.

3.                                      Except as set forth herein, the Investors’ Agreement shall remain in full force and effect in accordance with its terms.

4.                                      On or after the date hereof, each reference in the Investors’ Agreement to “this Agreement,” “hereunder,” “herein” or words of like import shall mean and be a reference to the Investors’ Agreement as amended hereby.  No reference to this Amendment No. 1 need be made in any instrument or document at any time referring to the Investors’ Agreement and a reference to the Investors’ Agreement in any such instrument or document shall be deemed a reference to the Investors’ Agreement as amended hereby.

5.                                      This Amendment No. 1 may be executed in any number of counterparts, all of which together shall constitute one instrument.

6.                                      This Amendment No. 1 shall be governed in all respects by the internal laws of the State of California as applied to agreements entered into among California residents to be performed entirely within California, without regard to principles of conflicts of law.

[signature page follows]

IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 1 to the Third Amended and Restated Investor Rights Agreement as of the date first written above.

INVESTORS:

See attached pages.

Agreed and Accepted:

IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 1 to the Third Amended and Restated Investor Rights Agreement as of the date first written above.

Signature Page to Kythera Biopharmaceuticals, Inc.

Amendment No. 1 to Third Amended and Restated Investor Rights Agreement

IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 1 to the Third Amended and Restated Investor Rights Agreement as of the date first written above.

Signature Page to Kythera Biopharmaceuticals, Inc.

Amendment No. 1 to Third Amended and Restated Investor Rights Agreement

IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 1 to the Third Amended and Restated Investor Rights Agreement as of the date first written above.

Signature Page to Kythera Biopharmaceuticals, Inc.

Amendment No. 1 to Third Amended and Restated Investor Rights Agreement

IN WITNESS WHEREOF, the parties hereto have executed this Amendment No. 1 to the Third Amended and Restated Investor Rights Agreement as of the date first written above.

Signature Page to Kythera Biopharmaceuticals, Inc.

Amendment No. 1 to Third Amended and Restated Investor Rights Agreement

Attachment 1

Schedule of Investors

(1)                                 Series C shares are issuable upon exercise of warrant dated March 21, 2011, as amended on August 30, 2011.

(2)                                 Series D shares are issuable upon exercise of warrant dated December 30, 2011.  Such warrant is initially exercisable for 114,109 shares and may be exercisable for up to 228,219 Series D shares.