Exhibit 10.15

THIRD AMENDMENT

TO

MASTER SERVICES AGREEMENT

THIS THIRD AMENDMENT to the MASTER SERVICE AGREEMENT (“Amendment”) is effective
as of January 29, 2014 (“Amendment Effective Date”), by and among EVOKE PHARMA,
INC. (“Client”) and SYNTERACTHCR, INC. (“SynteractHCR”).

RECITALS

WHEREAS, Client and SynteractHCR, Inc. (formally known as Synteract, Inc.)
entered into a Master Services Agreement dated January 30, 2009 and subsequent
Amendments, dated January 30, 2011 and November 25, 2013 (collectively the
“Agreement”); and

WHEREAS, Client and SynteractHCR wish to amend the terms of the Agreement as set
forth below.

NOW, THEREFORE, the parties agree to amend the Agreement as follows:

 

1. Section 5(a), entitled Term, will be deleted and replaced in its entirety
with the following:

“This Agreement shall commence on the Effective Date hereof (January 30, 2009)
and shall continue until January 30, 2017, unless and until terminated in
accordance with this Section 5”.

 

2. Except as expressly provided in this Amendment, all other terms, conditions
and provisions of the Agreement shall apply and remain in full force and effect.

 

3. Each individual signing for a corporate entity hereby personally warrants his
or her legal authority to bind that entity.

IN WITNESS WHEREOF, this Agreement is executed as of the Amendment Effective
Date

 

EVOKE PHARMA, INC.      SYNTERACTHCR, INC. By:  

/s/ David A. Gonyer

     By:  

/s/ Stewart Bieler

  Name: David A. Gonyer        Name: Stewart Bieler   Title: President and CEO
       Title: President, US Date: January 29, 2014      Date: January 29, 2014