FDA enforcement tracker: research-use-only peptide sellers

This page lists every warning letter we have found on fda.gov addressed to an online seller of peptide products that were labeled for research use. Each letter has been read in full. For each one we record what was offered, the disclaimer FDA quoted, and the kinds of evidence FDA cited to conclude that the products were intended for use in people. It is updated as new letters are published.

At a glance

Every letter quotes the seller's research-use disclaimer and then finds, from the rest of the evidence, that the products were drugs intended for use in people. In 2026 the pace increased: 11 letters, issued in batches on March 31, June 17 and August 24, 2026.

The letters

Newest first. Letters are identified by FDA's reference number and date; we do not name the sellers, and each letter can be found on fda.gov by its reference number. Products are listed as each letter names them.

What the letters cite

How often each kind of evidence appears across the 17 letters. Most letters cite several.

Evidence of intended use cited in the letters (our categories)

Evidence	What it covers	Letters
Effects in the body	Statements about effects on the body, such as appetite, blood sugar, body weight or disease	16 of 17 (94%)
Research framing	The same effects introduced as "studied for", "investigated for", "test subjects" or "preclinical models"	11 of 17 (65%)
Coded names	Abbreviated or coded product names, which the letter translates back to the substance	11 of 17 (65%)
Solvent	Bacteriostatic water offered alongside the peptides	11 of 17 (65%)
Clinical trials	Results, titles or citations of clinical trials	8 of 17 (47%)
Approved medicines	Brand names, statements that a substance is FDA-approved, or comparisons with approved products	5 of 17 (29%)
Social media or forum	Posts, videos or a community forum outside the store itself	4 of 17 (24%)
Syringes or kits	Syringes, or a kit pairing a solvent with a syringe	2 of 17 (12%)
Amounts or schedules	Amounts, schedules or protocols for use, on the site or in documents linked from it	2 of 17 (12%)
Calculators or guides	A "peptide calculator" or "peptide guide"	2 of 17 (12%)
Customer reviews	Customer reviews or testimonials displayed by the seller	1 of 17 (6%)
Laboratory-study summaries	Summaries of laboratory or animal studies presented as potential benefits	1 of 17 (6%)
Linked content	Third-party content hyperlinked from a product page	1 of 17 (6%)

Two categories deserve particular attention. In August 2026, one letter quoted a seller's summaries of laboratory studies, including cell-culture work, where they were presented as potential benefits, and another cited content from a public chemical database because the product page linked to it. In both cases what mattered was how the material was presented on the seller's site, not where it came from.

Substances named

The substances behind the products in the letters, counted once per letter. Coded names are counted as the substance the letter identifies.

Substances named in the letters

Substance	Letters
Retatrutide	14 of 17
Semaglutide	14 of 17
Tirzepatide	12 of 17
Bacteriostatic water	10 of 17
PT-141 (bremelanotide)	5 of 17
Tesamorelin	5 of 17
Cagrilintide	4 of 17
Mazdutide	4 of 17
SS-31 (elamipretide)	4 of 17
Ipamorelin	2 of 17
Survodutide	2 of 17
Gonadorelin	1 of 17
Prostamax	1 of 17
Sermorelin	1 of 17
Syringes	1 of 17

The solvent

11 of the 17 letters name bacteriostatic water offered alongside the peptides, including 10 of the 11 letters issued in 2026. In 9 letters FDA stated that the solvent was itself a drug, because of the peptides it was sold beside; in the others it was cited as evidence about the peptides, alongside syringes or a calculator. Of the 9 solvents found to be drugs, only one was sold under the designation for Injection; the others were sold as Bac water, Bacteriostatic Water 0.9% Benzyl Alcohol (10 ml), Reconstitution Solution (BAC), Bacteriostatic water for Peptides (BAC Water), BAC water, Bacteriostatic Water, BAC Water. The article on how FDA determines intended use explains the reasoning, and its limits.

Timeline

Letters by issue date

Issued	Letters	References
August 24, 2026	5	735127, 735067, 735063, 734884, 733652
June 17, 2026	1	729447
March 31, 2026	5	721806, 721805, 721709, 721600, 721088
February 26, 2025	1	696885
December 10, 2024	4	695663, 695607, 695156, 694608
February 7, 2024	1	668918

Scope and method

• Included: warning letters published on fda.gov, issued by FDA's Center for Drug Evaluation and Research, to online sellers of peptide products that carried a research-use or not-for-human-consumption disclaimer which FDA quoted in the letter.
• How we search: FDA's warning letter index, for peptide-related terms and for the names of the substances that appear in the letters. Every candidate letter is read in full before it is included.
• Excluded: letters to compounding pharmacies, telehealth providers, online pharmacies, manufacturers and approved-product sponsors, which raise different issues; and letters to research-labeled sellers of products that are not peptides. The letter of Jun 12, 2023 (ref. 655280) was excluded because it concerns selective androgen receptor modulators (SARMs), not peptides. The letter of Dec 12, 2025 (ref. 719337) was excluded because it concerns selective androgen receptor modulators (SARMs), not peptides, despite the name.
• Not covered: FDA describes advisory notifications that are not necessarily published, and untitled letters, import actions and prosecutions are recorded elsewhere. This page is a minimum, not a complete count of FDA activity.
• Categories: the evidence categories are ours, assigned by reading each letter. A category is marked only where the letter itself quotes or describes that kind of evidence.
• Last checked: October 22, 2026.

Frequently asked questions

Does a warning letter mean a company broke the law?

It means FDA considers that it did. A warning letter is, in FDA's words, informal and advisory, and it is not final agency action. Only a court can finally decide whether the law was broken.

Why are only some letters included?

The tracker covers one situation: online sellers of peptide products labeled for research use. Letters about compounding, telehealth, online pharmacies or manufacturing quality raise different questions and are left out.

Is this every action FDA has taken?

No. It covers published warning letters only. FDA also sends advisory notifications that are not necessarily posted, and uses import alerts and referrals for prosecution.

Will FDA's approach stay the same?

Not necessarily. These letters reflect FDA's current interpretation and priorities, which can change, and the regulations themselves are revised from time to time.

Sources & Further Reading

1. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 668918. February 7, 2024.
2. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 694608. December 10, 2024.
3. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 695156. December 10, 2024.
4. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 695607. December 10, 2024.
5. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 695663. December 10, 2024.
6. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 696885. February 26, 2025.
7. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 721088. March 31, 2026.
8. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 721600. March 31, 2026.
9. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 721709. March 31, 2026.
10. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 721805. March 31, 2026.
11. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 721806. March 31, 2026.
12. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 729447. June 17, 2026.
13. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 733652. August 24, 2026.
14. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 734884. August 24, 2026.
15. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 735063. August 24, 2026.
16. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 735067. August 24, 2026.
17. Food and Drug Administration, Center for Drug Evaluation and Research. Warning letter, reference 735127. August 24, 2026.
18. Food and Drug Administration. Regulatory Procedures Manual, Chapter 4: Advisory Actions (Warning Letters and Untitled Letters).
19. 21 CFR 201.128, Meaning of "intended uses".