Exhibit 5.1

May 26, 2016

The Board of Directors of Cancer Prevention Pharmaceuticals, Inc.

1760 East River Road, Suite 250

Tucson, Arizona 85718

Re: Registration Statement on Form S-1 (File No. 333-208718)

Ladies and Gentlemen:

We have acted as U.S. securities counsel to Cancer Prevention Pharmaceuticals, Inc., a Delaware corporation (the “Company”), in connection with the preparation and filing with the Securities and Exchange Commission (the “Commission”) pursuant to the Securities Act of 1933, as amended (the “Securities Act”), of a Registration Statement on Form S-1 (File No. 333-208718) (as amended through the date hereof, the “Registration Statement”) pertaining to the issuance and sale by the Company of shares of common stock, par value $0.001 (the “Common Stock”), with a proposed maximum aggregate offering price of $18,687,500 (the “Shares”), including shares of Common Stock issuable upon the exercise of an over-allotment option granted by the Company to the underwriters to purchase additional shares of Common Stock. The Shares are to be sold by the Company pursuant to an underwriting agreement (the “Underwriting Agreement”) to be entered into by and between the Company and Aegis Capital Corp., the form of which has been filed as Exhibit 1.1 to the Registration Statement. The Company is also registering warrants to purchase shares of Common Stock of the Company to be issued to the representative of the underwriters as additional compensation pursuant to the Underwriting Agreement (the “Representative’s Warrant”), as well as the shares of Common Stock issuable upon exercise of the Representative’s Warrant (the “Representative’s Warrant Shares”), with a proposed maximum aggregate offering price of $893,750.

In rendering the opinion set forth herein, we have examined originals or copies, certified or otherwise identified to our satisfaction, of such documents, corporate records, certificates of public officials and other instruments as we have deemed necessary or advisable.

In such examination, we have assumed the genuineness of all signatures, the legal capacity of natural persons, the authenticity of all items submitted to us as originals, the conformity with originals of all items submitted to us as copies, and the authenticity of the originals of such copies. As to any facts material to the opinions expressed herein that we did not independently establish or verify, we have relied upon statements and representations of officers and other representatives of the Company and public officials.

This opinion is based solely on the General Corporation Law of the State of Delaware (including all related provisions of the Delaware Constitution and all reported judicial decisions interpreting the General Corporation Law of the State of Delaware and the Delaware Constitution) and the laws of the State of New York as they relate to the Representative’s Warrant.

Cancer Prevention Pharmaceuticals, Inc.

May 26, 2016

Page 2

Based upon and subject to the foregoing, we are of the opinion that: (i) the Shares have been duly authorized for issuance and, when issued, delivered and paid for in accordance with the terms of the Underwriting Agreement, the Shares will be validly issued, fully paid and non-assessable; (ii) the Representative’s Warrant, when executed and delivered by the Company in accordance with and in the manner described in the Registration Statement and the Underwriting Agreement, will constitute a valid and binding agreement of the Company enforceable against the Company in accordance with its terms, subject to applicable bankruptcy, insolvency, fraudulent conveyance, moratorium and similar laws affecting creditors’ rights generally and equitable principles of general applicability; and (iii) the Representative’s Warrant Shares, when issued and sold by the Company and delivered by the Company upon valid exercise thereof and against receipt of the exercise price therefor, in accordance with and in the manner described in the Registration Statement and the Representative’s Warrant, will be validly issued, fully paid and non-assessable.

We consent to the inclusion of this opinion as an exhibit to the Registration Statement and further consent to all references to us under the caption “Legal Matters” in the Prospectus. In giving this consent, we do not admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations of the Commission.

	Very truly yours,

	/s/ Gracin & Marlow, LLP
	Gracin & Marlow, LLP

Cancer Prevention Pharmaceuticals, Inc. S-1/A