POWER OF ATTORNEY
Know all by these presents, that the undersigned hereby constitutes
and appoints each of Paul Brannelly and Michael T. Heffernan, with full power
to act singly, as the undersigned's true and lawful attorney-in-fact with full
power of substitution to:
(1) execute for and on behalf of the undersigned, in the
undersigned's capacity as an officer and/or director and/or beneficial owner
of Collegium Pharmaceutical Inc. (the "Company"), Form ID Application,
Forms 3, 4 and 5 in accordance with Section 16(a) of the Securities Exchange Act
of 1934, as amended and the rules thereunder;
(2) do and perform any and all acts for and on behalf of the
undersigned which may be necessary or desirable to complete and execute
any such Form ID Application, Forms 3, 4 or 5, complete and execute any
amendment or amendments thereto and timely file such forms with the
United States Securities and Exchange Commission and any stock exchange
or similar authority; and
(3) take any other action of any type whatsoever in connection
with the foregoing which, in the opinion of such attorney-in-fact, may be of
benefit to, in the best interest of, or legally required by, the undersigned,
it being understood that the documents executed by such attorney-in-fact
on behalf of the undersigned pursuant to this Power of Attorney shall be in
such form and shall contain such terms and conditions as such attorney-in-fact
may approve in such attorney-in-fact's discretion.
The undersigned hereby grants to the attorney-in-fact full power and
authority to do and perform any and every act and thing whatsoever requisite,
necessary or proper to be done in the exercise of any of the rights and powers
herein granted, as fully to all intents and purposes as the undersigned might
or could do if personally present, with full power of substitution or revocation,
hereby ratifying and confirming all that such attorney-in-fact, or such
attorney-in-fact's substitute or substitutes, shall lawfully do or cause to be
done by virtue of this power of attorney and the rights and powers herein
granted.
This power of attorney shall remain in full force and effect until
revoked by the undersigned in a signed writing delivered to the attorney-in-fact.
IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney
to be executed as of the 23rd day of April, 2015.
/s/Gino Santini
Name: Gino Santini
Title: Director
