FDA Tells Five 'Research Use Only' Peptide Sellers Their Products Are Unapproved Drugs

A "research use only" label does not make it lawful to sell peptides for human use. That is the message of five FDA warning letters dated 24 August 2026 and posted on 1 September, which tell online sellers that their semaglutide, tirzepatide, retatrutide and other peptide products are unapproved new drugs.

Who received the letters

The letters come from FDA's Center for Drug Evaluation and Research, and each follows a July 2026 review of the seller's website. They went to Peak Performance Peptides, Royal Peptides LLC, NuScience Peptides LLC, Peptide Partners LLC and TXP Innovations LLC dba Tex Peptides.

The products named across the five letters include semaglutide, tirzepatide, retatrutide, SS-31 (elamipretide), PT-141 (bremelanotide) and tesamorelin; the NuScience letter adds survodutide and mazdutide. Several letters also list bacteriostatic water.

The core legal sentence recurs almost word for word. In the Peak Performance letter: "Despite statements on your product labeling marketing your products for 'research use only' and 'not for human consumption,' evidence obtained from your website establishes that your products are intended to be drugs for human use." FDA points to intended use as defined in 21 CFR 201.128, and concludes the products are "new drugs" under section 201(p) because they are not generally recognised as safe and effective, adding that "No approved applications pursuant to section 505 of the FD&C Act are in effect for these products." Introducing them into interstate commerce, the letters say, violates sections 301(d) and 505(a).

The evidence FDA cites is the websites' own content. The NuScience letter quotes survodutide product copy claiming "Efficacy in promoting weight loss and improving glycemic control." The Royal Peptides letter says the firm markets "bacteriostatic water alongside a 'peptide guide' and 'peptide calculator,' resources that collectively provide the means to prepare an injectable drug for human administration."

FDA's own characterisation of risk, stated in the Peak Performance letter, is that "Injectable drug products can pose risks of serious harm to users," because they "bypass some of the body's key defenses against toxins and microorganisms." Each firm was given 15 business days to respond.

A pattern through 2026

The August letters were not the first this year. FDA used the same reasoning in a 31 March 2026 letter to Gram Peptides (retatrutide, tirzepatide and bacteriostatic water) and a 17 June 2026 letter to Wholesale Peptide (Prostamax and gonadorelin). Both addressed "research use only" and "not for human consumption" labelling.

The enforcement is not limited to online sellers. On 18 September the agency also warned a Texas compounding pharmacy over vitamin-added semaglutide and tirzepatide products — a separate legal route, covered in our report on that letter.

What this does not say

• It is not a court ruling. FDA's Regulatory Procedures Manual says a warning letter "is informal and advisory," does not commit the agency to enforcement action, and is not considered final agency action. Each letter warns that failure to correct may bring action "including, without limitation, seizure and injunction."
• It does not mention BPC-157 or TB-500. None of the five August letters, nor the March and June letters, names either compound. Their status is covered separately on our FDA status page.
• It does not set a new rule. The letters apply existing statutory provisions to specific websites; they are not rulemaking and do not change any compounding list.
• It is not a finding about the recipients' products beyond what is written. FDA notes its letters are not "an all-inclusive list of the violations." Firms may respond, and FDA says it may issue a close-out letter only once corrective actions have actually been made and verified.

Related

• Are Peptides Legal in the US?
• Compounding Is Not FDA Approval
• FDA warning letter calls Empower Pharmacy's vitamin-added GLP-1 compounds "essentially copies"
• FDA status tracker
• BPC-157
• TB-500