FDA rejects 'research use only' labels: warning letters to five peptide sellers

What FDA sent and to whom

On August 24, 2026, the Center for Drug Evaluation and Research (CDER) at the U.S. Food and Drug Administration dated warning letters to five online sellers: Peak Performance Peptides (reference 735127), Royal Peptides LLC (734884), NuScience Peptides LLC (733652), Peptide Partners LLC (735063) and TXP Innovations LLC, doing business as Tex Peptides (735067). The letters are signed by CDER's Office of Unapproved Drugs and Labeling Compliance, and FDA's public pages show content current as of September 1, 2026¹²³⁴⁵.

The agency reviewed the companies' websites in July 2026 and concluded they were offering unapproved new drugs. It cites sections 201(g)(1), 201(p), 301(d) and 505(a) of the Federal Food, Drug, and Cosmetic Act, plus the intended-use rule, 21 CFR 201.128. Each company has 15 business days from receipt to respond to FDAAdvisory@fda.hhs.gov¹³⁵.

The footnote: why 'research use only' did not hold

The core is footnote 1 of the Tex Peptides letter. It quotes the company's labeling, which says 'research use only,' 'for research and laboratory use only' and 'not for human or veterinary use,' and answers: 'Despite statements on your product labeling marketing your products “research use only”, “for research and laboratory use only”, and “not for human or veterinary use,” evidence obtained from your website establishes that your products are intended to be drugs for human use.'¹

The Peptide Partners letter uses a nearly identical footnote, quoting 'for research use only' and 'not for human or veterinary use'⁴. In the Royal Peptides, NuScience and Peak Performance letters, FDA quotes each firm's own variant of the disclaimer ('for research use only,' 'not for human or animal consumption,' 'not intended for human or veterinary use') and reaches the same conclusion²³⁵.

This is not a new test. The intended-use rule refers to 'the objective intent of the persons legally responsible for the labeling of an article,' which 'may, for example, be shown by labeling claims, advertising matter, or oral or written statements,' or by the circumstances of distribution¹². A prior wave of seven letters, reported in April 2026, had already applied that logic to 'research use only' tirzepatide and semaglutide sellers⁹.

What counted as evidence of human use

The letters rest on site content, not the label. Examples cited include product descriptions framed around weight, glycemic control, sexual function or mitochondrial function²³⁵; the Tex Peptides letter quotes claims such as 'the management of type 2 diabetes, obesity, and metabolic disorders'¹.

A second element is bacteriostatic water. The Tex Peptides, NuScience and Peak Performance letters say it was sold as a solvent to reconstitute the peptides, which FDA says provides the means to prepare an injectable drug; FDA treats the water as a drug for the same reason¹³⁵. The Royal Peptides letter adds that the company marketed the water alongside a 'peptide guide' and a 'peptide calculator,' and the NuScience letter mentions the calculator²³.

For clinical readers, the practical point is that FDA reads the whole picture: product page, supporting material, companion products and sales context. A law firm that analyzed the letters recommends auditing sites against the intended-use standard and concludes that a research-use-only disclaimer will not overcome dosing or human-use content⁸.

Which peptides were named, and which were not

Taken together, the letters name semaglutide, tirzepatide and retatrutide, plus tesamorelin, SS-31 (elamipretide) and PT-141 (bremelanotide). NuScience adds survodutide, mazdutide and a tesamorelin + ipamorelin blend; Royal Peptides, a product called 'BIMORELIN'¹²³⁵. The Peak Performance letter states that no approved applications under section 505 are in effect for those products⁵.

The science behind these names is uneven. Semaglutide and tirzepatide have large published obesity trials¹³¹⁴; retatrutide has a phase 2 trial¹⁵ and was described in April as an investigational drug⁹; an elamipretide product from Stealth BioTherapeutics received accelerated approval for Barth syndrome in September 2025¹⁶. The letters do not dispute that science: they address products the sellers offer without an approved application.

How it sits next to the July vote

On July 23 and 24, 2026, the Pharmacy Compounding Advisory Committee (PCAC) recommended six peptides for the 503A bulks list: BPC-157, KPV, TB-500, MOTS-c, Semax and Epitalon⁶. Reports say BPC-157, KPV and TB-500 passed 8-6 and MOTS-c 7-5; the vote is nonbinding and requires formal rulemaking¹⁰¹¹. FDA scientists cited insufficient data and said the peptides are poorly characterized, and there were conflict-of-interest objections about some members¹⁰¹¹.

None of those six appears in the August letters, and none has been added to the list yet⁶⁸. In other words, FDA is acting against sellers of other peptides while the regulatory process for those six remains open⁶⁸. The next PCAC meeting, expected before February 2027, will consider LL-37, GHK-Cu, dihexa, Melanotan II and PEG-MGF⁶.

What it means for labeling and sourcing claims

• Label wording is not the deciding factor: FDA reads the entire website¹¹².
• Dosing material, calculators and reconstitution products sold next to the peptide were cited as evidence in the letters¹²³.
• The letters warn of possible further action; one outlet that covered them quotes 'seizure, and injunction'⁷.
• When evaluating a supplier, review what its site says and offers, not just the label disclaimer⁸.

This analysis is regulatory journalism, not a recommendation for use. Research products are not intended for human or veterinary use.