Exhibit 99.1

13G

CUSIP No. 36870A108

AGREEMENT

Pursuant to Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended, the undersigned hereby agree that only one statement containing the information required by Schedule 13G need be filed with respect to the ownership by each of the undersigned of Common Stock of Gemphire Therapeutics Inc.

Dated:	February 7, 2017
EXCEL VENTURE FUND II, L.P.
BY:	EXCEL VENTURES II GP, LLC
ITS:	GENERAL PARTNER
By:	/s/ Steven R. Gullans
	Manager

EXCEL VENTURES II GP, LLC

/s/ Steven R. Gullans

Manager

/s/ Frederick R. Blume

Frederick R. Blume

/s/ Steven R. Gullans

Steven R. Gullans

/s/ Juan Enriquez

Juan Enriquez

/s/ Caleb Winder

Caleb Winder

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