The letters are dated August 24, 2026 and appeared in the FDA's warning letter database the following week. Five of them, to five US companies that sell peptides online: Peak Performance Peptides, Royal Peptides, NuScience Peptides, Peptide Partners, and TXP Innovations, which trades as Tex Peptides. All five came from the same office, the Center for Drug Evaluation and Research's Office of Unapproved Drugs and Labeling Compliance, and all five carry the same subject line: Unapproved New Drugs/Misbranded.
Between them the letters name semaglutide, tirzepatide, retatrutide, survodutide, mazdutide, SS-31, PT-141, tesamorelin, and a tesamorelin and ipamorelin blend. Four of the five also cite bacteriostatic water sold for reconstitution, which the agency classified as a drug in its own right.
The argument is about intended use
None of this is a purity story. The FDA did not say the material was fake, underdosed, or contaminated, and it did not test anything. The theory in every letter is intended use: the agency decides what a product is for by looking at how it is sold, and a website can make that decision for you.
The sentence that recurs across the letters is that evidence from the company's website "establishes that your products are intended to be drugs for human use." Once a product is a drug in the agency's eyes, selling it without an approved application makes it an unapproved new drug, and labeling that does not carry adequate directions for use makes it misbranded. The words "research use only" on the label do not change either conclusion if everything around the label says otherwise.
What counted as evidence
The letters are specific about what the agency read. Claims about weight loss, glucose control, and disease. Summaries of clinical trial results placed next to a buy button. The phrase "once-weekly injection" and dose arithmetic. Bundled kits that combine several compounds. Peptide calculators and guides. Bacteriostatic water and insulin syringes listed alongside the vials. Links out to PubChem entries. Each of these, on its own, is ordinary content for this corner of the internet. Together, in the agency's reading, they describe a product meant to go into a person. A seller can keep the label clean and still tell the FDA exactly what the product is for, one blog post and one dosing calculator at a time.
What happens next
A warning letter is not a fine or a seizure. It is a formal notice that the agency believes the law is being broken, with a request to correct the violations and reply, typically within fifteen working days. Companies that do not respond, or respond badly, can face seizure, injunction, or referral. Several of the five sites were still live at the time of writing.
For readers, the practical lesson runs in the other direction. The same content the FDA used as evidence is content you can read before you buy. A site that tells you how much to take and what will happen when you do has told the regulator what it is selling. A site that publishes a lab report and stops there has made a narrower claim, and a checkable one.
This publication covers the published science of these compounds as a field. It does not tell anyone what to do with a vial, and the material its publisher sells is for laboratory research only.
Sources: FDA warning letters dated August 24, 2026 to Peak Performance Peptides, Royal Peptides LLC, NuScience Peptides LLC, Peptide Partners LLC and TXP Innovations LLC, published in the FDA warning letters database, September 2026.
For research use only · Not for human or veterinary use · No compound discussed here is FDA-approved for any indication