Exhibit 5.1

Joshua D. Brinen  Attorney at Law New York Office jbrinen@brinenlaw.com   Member New York, New Jersey, Florida, California, Texas & Nevada Bar LL.M. in Taxation

December 19, 2025

VIA EDGAR SUBMISSION ONLY

ProPhase Labs, Inc.

626 RXR Plaza, 6th Floor

Uniondale, New York 11556

To Whom It May Concern:

We have acted as counsel to ProPhase Labs, Inc., a Delaware corporation (the “Company”), in connection with the offer and sale from time to time by the Company of our common stock having an aggregate offering price of up to $4,265,221 shares (the “Shares”), par value $0.0005 per share, pursuant to that certain At-the-Market Offering Sales Agreement dated as of October 9, 2025 (the “Sales Agreement”), by and between the Company and WestPark Capital, Inc. (the “Sales Agent”). The shares will be offered and sold pursuant to the prospectus supplement dated October 15, 2025 (the “Prospectus Supplement”), filed by the Company with the Securities and Exchange Commission (the “Commission”) pursuant to Rule 424(b)(5) under the Securities Act of 1933, as amended (the “Securities Act”), supplementing the prospectus dated November 20, 2024 (the “Base Prospectus”), that forms part of the Company’s shelf registration statement of Form S-3 (File No. 333-283182) (the “Registration Statement”).

As counsel for the Company, in rendering this opinion, we have examined and relied upon originals or copies, certified or otherwise identified to our satisfaction, of the Registration Statement, the Base Prospectus, the Prospectus Supplement, the Company’s Amended and Restated Certificate of Incorporation (the “Charter”) and Amended and Restated Bylaws (the “Bylaws”), resolutions of the Company’s Board of Directors authorizing the Sales Agreement and the issuance and sale of the Shares, and such other corporate records, certificates, and documents as we have deemed necessary or appropriate for the purpose of this opinion. 

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, we have relied upon statements and representations of officers and other representatives of the Company and public officials.

Based upon the foregoing and subject to the assumptions, qualifications and limitations set forth below, we are of the opinion that:

We express no opinion herein as to any laws other than the General Corporation Law of the State of Delaware and the federal laws of the United States of America that, in our experience, are normally applicable to transactions of the type contemplated by the Sales Agreement. This opinion is rendered as of the date hereof, and we assume no obligation to update or supplement this opinion to reflect any facts or circumstances that may hereafter come to our attention or any changes in law that may occur after the date hereof. We do not find it necessary for the purposes of this opinion letter to cover, and accordingly we express no opinion as to, the application of the securities or blue-sky laws of the various states to the sales of the Shares.

We hereby consent to the filing of this opinion as Exhibit 5.1 to the Prospectus Supplement and to the reference to our firm under the caption “Legal Matters” in the Prospectus and the Prospectus Supplement. In giving this consent, we do not admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act or the rules and regulations promulgated thereunder.

Should you have any questions, please do not hesitate to contact me at the New York office or via electronic mail at jbrinen@brinenlaw.com.

JDB:sem