Exhibit 5.1

October 2, 2018

PetIQ, Inc.

923 S. Bridgeway Place

Eagle, Idaho 83616

Ladies and Gentlemen:

We have acted as special counsel to PetIQ, Inc., a Delaware corporation (the “Company”), in connection with the preparation and filing with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Securities Act”), of (i) the registration statement on Form S-3 (File No. 333-227186) (the “Registration Statement”) initially filed with the Commission on September 4, 2018, (ii) the base prospectus dated September 21, 2018 forming a part of the Registration Statement (the “Base Prospectus”) and (iii) the final prospectus supplement dated September 26, 2018 in the form filed with the Commission pursuant to Rule 424(b) under the Securities Act on September 27, 2018 (together with the Base Prospectus, the “Prospectus Supplement”) in connection with the offering by (i) the Company of 2,000,000 shares (the “Primary Shares”) of the Company’s Class A common stock, par value $0.001 per share (the “Class A Common Stock”), covered by the Registration Statement and (ii) certain selling stockholders named in the Prospectus Supplement (the “Selling Stockholders”) of 3,750,000 shares of Class A Common Stock (the “Secondary Shares” and together with the Primary Shares, the “Shares”). The Shares are being sold pursuant to the Underwriting Agreement, dated September 26, 2018 (the “Underwriting Agreement”), by and among the Company, PetIQ Holdings, LLC (“Holdco” and together with the Company, the “PetIQ Parties”) the Selling Stockholders and Jefferies LLC, as the representative of the underwriters named in Schedule I thereto (the “Underwriters”). We understand that the Shares are to be offered and sold in the manner described in the Prospectus Supplement.

This opinion letter is being delivered in accordance with the requirements of Item 601(b)(5) of Regulation S-K promulgated under the Act.

In rendering the opinion set forth below, we have examined and relied upon such certificates, corporate records, agreements, instruments and other documents that we considered necessary or appropriate as a basis for the opinion, including (i) the Registration Statement, (ii) the Prospectus Supplement and (iii) the Underwriting Agreement. In our examination, we have assumed the legal capacity of all natural persons, the genuineness of all signatures, the authenticity of all documents submitted to us as certified or photostatic copies, the authenticity of the originals of such latter documents and that the Underwriting Agreement constitutes the valid and binding obligation of each party thereto (other than the PetIQ Parties) enforceable against each such party in accordance with its terms. As to any facts material to this opinion that we did not independently establish or verify, we have relied upon oral or written statements and representations of officers and other representatives of the Company and others.

Based upon the foregoing and subject to the assumptions, qualifications and limitations set forth herein, we are of the opinion that (i) the Primary Shares have been duly authorized and, when the Primary Shares are delivered to the Underwriters against payment of the agreed consideration therefor in accordance with the Underwriting Agreement, the Primary Shares will be validly issued, fully paid and nonassessable, and (ii) the Secondary Shares have been duly authorized and are validly issued, fully paid and nonassessable.

The foregoing opinion is limited to the General Corporation Law of the State of Delaware (including the statutory provisions, the applicable provisions of the Delaware Constitution and reported judicial decisions interpreting the foregoing). We express no opinion with respect to any other laws, statutes, regulations or ordinances.

We hereby consent to the filing of this opinion as an exhibit to the Company’s Current Report on Form 8-K to be filed with the Commission on October 2, 2018 and its incorporation by reference into the Registration Statement and to the reference to our firm under the caption “Legal Matters” in the Prospectus Supplement included in the Registration Statement. In giving such consent, we do not concede that we are experts within the meaning of the Securities Act or the rules and regulations thereunder or that this consent is required by Section 7 of the Securities Act.