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 research use only peptides are unapproved new drugs.

Research use only peptides: 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, 21 U.S.C. 355, 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.

What each letter cites

Each letter names the website FDA reviewed, lists the products it considers unapproved new drugs, and quotes the product pages it relied on. The summaries below describe only what the letters themselves say.

• Peak Performance Peptides (website pppepz.com). Products named: "Bac water," "GLP-3R" (retatrutide), "Semaglutide," "SS-31," "PT-141," and "Tesamorelin". Among the lines FDA quotes from the retatrutide page: "Explored for potential impact on body weight and fat distribution". A footnote notes that many of the products "are offered in different strengths."
• Royal Peptides LLC (royal-peptides.com). Products named: "Tirzepatide," "Semaglutide," "Retatrutide," "SS-31 (Elamipretide)," "PT-141," "Tesamorelin" and "BIMORELIN", which the site describes as "a cutting-edge dual peptide blend combining Tesamorelin (10mg) and Ipamorelin (3mg)." FDA quotes the SS-31 page: "Advanced Research Use: Mitochondrial repair, anti-aging, neuroprotection." The letter also cites comparison articles on the site, not just product listings.
• NuScience Peptides LLC (nusciencepeptides.com). Nine products are named, including "GLP-2 Tirz Peptide," "GLP-1 Sema Research Peptide," "Survodutide," "Mazdutide," "Tesamorelin Ipamorelin Blend," and "Bacteriostatic water for Peptides (BAC Water)". FDA quotes the tesamorelin page: "research indicates that tesamorelin may enhance cognitive function, including improvements in executive function and verbal memory." For the semaglutide product, the quoted text comes from a PubChem page that the letter says was "hyperlinked from" the firm's product page.
• Peptide Partners LLC (peptide.partners). Products named: "GLP-1 S (Semaglutide)," "GLP-2 T (Tirzepatide)," "GLP-3 Reta (Retatrutide)," "SS-31 (Elamipretide)," "Tesa Peptide (Tesamorelin)," "PT-141 (Bremelanotide)," and "Reconstitution Solution (BAC)". Much of the quoted copy summarises laboratory studies; on the PT-141 page FDA quotes: "This study discovered that bremelanotide can kill brain cancer cells (glioblastoma) grown in laboratory culture dishes without harming normal cells."
• TXP Innovations LLC dba Tex Peptides (texpeptide.com). Products named: "Semaglutide (GLP-1 SEM)," "Tirzepatide (GLP-2 TRZ)," "Retatrutide (GLP-3 RT)," "SS-31 (Elamipretide)," "Tesamorelin," "PT-141 (Bremelanotide)," and "Bacteriostatic Water 0.9% Benzyl Alcohol (10 ml)". FDA quotes the PT-141 page: "It’s an effective and powerful enhancer for both mood and your senses."

The disclaimers FDA set aside differ slightly from site to site. According to the letters, the firms' labelling used phrases including "not for human or animal consumption" (Royal Peptides), "for laboratory, research, and analytical use" and "not intended for human or veterinary use" (NuScience), "not for human or veterinary use" (Peptide Partners) and "for research and laboratory use only" (Tex Peptides). In each case FDA concluded that "evidence obtained from your website establishes that your products are intended to be drugs for human use."

FDA also counts the bacteriostatic water as a drug. In the four letters that list it as a product, FDA says the firm sells it "to be used to reconstitute the peptide products sold on your website," and that "The sale of these products together demonstrates" it is intended "to be used in combination for injection." The NuScience letter adds that the firm markets it "alongside a 'peptide calculator,' a resource that provides the means to prepare an injectable drug for human administration."

What "intended use" means

The letters turn on intended use. Each says the website examples "provide evidence of the intended use (as defined in 21 CFR 201.128) of these products as drugs." That regulation, in the wording FDA published in the Federal Register on 2 August 2021, says intended uses "refer to the objective intent of the persons legally responsible for the labeling of an article (or their representatives)."

The same text says this intent "may, for example, be shown by labeling claims, advertising matter, or oral or written statements by such persons or their representatives," and may also be shown by "the circumstances surrounding the distribution of the article." That is why the letters quote product descriptions and study summaries rather than the disclaimers: under this reading, what a seller says about a product, and what it sells alongside it, can outweigh a "research use only" statement.

What the firms are asked to do

The closing section of each letter sets out the same requests. FDA says each firm is "responsible for investigating and determining the root causes of any violations and implementing corrective and preventative measures." The written response goes to FDAAdvisory@fda.hhs.gov and should "Include the specific steps you have taken to correct any violations, an explanation of each step being taken to prevent the recurrence of violations, as well as copies of related documentation."

A firm that disagrees can say so. Each letter states: "If you have information that you believe demonstrates that your products are not in violation of the FD&C Act and FDA regulations, include that information for our consideration." None of the five letters sets out a firm's response, and the letters do not say whether any product has been removed from sale.

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.

This article reports regulatory actions. It is not legal or medical advice.

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