On March 31, 2026, the FDA issued a batch of warning letters to online peptide sellers. Read together, they are less a series of individual actions than a single, clearly stated argument: a “research use only” label does not determine a product’s regulatory status when the rest of a seller’s evidence points to human use.
The core reasoning
Each letter follows the same structure. The agency reviews a seller’s website, observes that it offers peptides for sale, and then cites the seller’s own material — product pages, marketing copy, linked resources — as evidence of intended use under 21 CFR 201.128. That regulation is explicit that intended use may be shown by “the circumstances surrounding the distribution of the article,” not merely by what a label says. Where the surrounding evidence establishes that a product is intended to treat disease or affect the structure or function of the body, the product is a drug — and an unapproved one.
The letters are direct on the point that disclaimers do not cure this. In the agency’s words, the RUO and “not for human consumption” statements did not control, because other evidence established an intended human-drug use.
Two patterns worth separating
The letters illustrate two distinct ways a seller supplies that evidence.
In one, the seller’s own website copy did the work. Product pages described appetite suppression, weight reduction, and improved glucose handling — language describing effects on the human body. No external material was needed; the store’s marketing was the evidence.
In the other, the evidence lived in a linked property. The agency noted that a seller’s website linked to a community forum, then cited that forum’s “cheat sheet” — with dosing and titration schedules — as establishing intended use. The separate location of the content did not separate it from the seller. The linked resource became part of the case.
Why it matters beyond these firms
The through-line is that the agency evaluated the totality of each seller’s presentation — website, marketing, and linked material — rather than accepting a label at face value. For anyone operating in or observing this market, the letters are a map of what constitutes intended-use evidence: benefit claims, dosing guidance, and the connective tissue between educational content and a point of sale.
The letters are a snapshot, not a comprehensive statement of the law, and each names an opportunity to respond. But the reasoning is consistent with how intended use has long been defined, and it should be read as a description of how these cases are built.