The law defines a drug by its intended use, and judges that intent objectively. In practice, that judgment is made by FDA staff reading a seller's website. Their findings are published. Between February 2025 and August 2026, FDA's Center for Drug Evaluation and Research issued a run of warning letters to online peptide sellers whose products carried research-use-only disclaimers. Read together, the letters show with unusual clarity what the agency looks at, what it quotes, and what it does not accept.
Interpretation, not settled law. FDA's warning letters record the agency's reading of the law as applied to particular facts at a particular time. In FDA's own words, a warning letter is informal and advisory
, and the agency does not consider Warning Letters to be final agency action
. The positions described here are a guide to how FDA currently interprets the Act and its regulations, not rulings of a court, and that interpretation, the agency's enforcement priorities and the regulations themselves can change. Everything in this article describes how FDA has reasoned in these cases; none of it guarantees how the agency, or a court, will reason in the next one.
How cases begin
Most of these letters open the same way: FDA reviewed the seller's website, on stated dates, and documented what it found. Nothing in them suggests a complaint, a sample or an inspection was needed. The website was enough.
Our office conducts surveillance to identify distribution of unapproved or misbranded drugs sold online, as well as misleading labeling practices.
Several features of the record stand out:
- Letters arrive in sweeps. At least four letters to peptide sellers are dated March 31, 2026, and at least five are dated August 24, 2026. The August letters each record a website review in July 2026.
- The interval is short. Letters followed the documented reviews within weeks to a few months.
- Prior notice is not required. FDA's compliance office notes that, outside a few defined areas, it is not required to hold a meeting or give any other prior notice before taking enforcement action.
- Not everything is public. The same report describes advisory notifications sent to companies to prompt correction, and notes that these are not necessarily posted. The published letters are the visible part of the activity.
- The tools are changing. In June 2025 FDA launched an agency-wide generative AI tool, which it said was already being used, among other things, to identify high-priority inspection targets.
The evidence FDA cites
Every letter in this series follows the same legal path: the products are drugs under section 201(g)(1) because of their intended use; they are new drugs under section 201(p); and selling them without approval violates sections 301(d) and 505(a). What differs from letter to letter is the evidence of intended use. It falls into recognisable categories.
| Category | What the letters quote |
|---|---|
| Direct claims about the body | Appetite, blood sugar, body weight and similar effects, often with figures from clinical trials |
| Research-framed claims | The same effects introduced as "studied for", "investigated for" or "researched for", including in "preclinical models" |
| Approved medicines and brand names | Brand names in product titles, statements that a substance is FDA-approved, comparisons with approved products |
| Coded product names | Names such as "GLP-1 S", "GLP-2 TZ" or "GLP-3 RT", which the letters translate back to the active ingredient |
| Accompanying solvents | Bacteriostatic water offered alongside peptide products, found to be a drug itself |
| Kits and equipment | A kit pairing a solvent with a syringe |
| Calculators and guides | A "peptide calculator" and "peptide guide", described as providing the means of preparation for use in people |
| Categorisation of known drug substances | Neutral-sounding category text for the active ingredients of approved medicines, quoted alongside other claims |
Direct claims
The most obvious evidence is the most common. Product pages described effects on appetite, glucose and body weight, frequently borrowing results from clinical trials of approved medicines.
This cutting-edge peptide has shown jaw-dropping results in clinical trials — helping the body torch fat, suppress appetite, regulate blood sugar, and even improve metabolic function better than its single-pathway competitors.
Research framing does not neutralise a claim
Many sellers have learned to put effects into research language. The letters show that the framing does not change what is being described. FDA quoted, as evidence of intended use:
Metabolic Regulation – Studied for its ability to lower glucose and support balanced insulin levels.
Semaglutide has been investigated for its influence on insulin secretion, satiety pathways, and body weight management. It is commonly considered in preclinical models exploring endocrine signaling, diabetes, and obesity-related research.
"Studied for" is still a statement about what a product does to the body. The agency reads the effect, not the verb in front of it.
Approved medicines and their names
Product titles that included a brand name, and statements that a substance was approved, were cited directly. The letters then point out that an approval covers a specific product from a specific company, not every vial of the same molecule:
While there are FDA-approved tirzepatide products on the market in the U.S., there are no approved drug applications pursuant to section 505 of the FD&C Act in effect for the 5mg Tirzepatide (Mounjaro) 5mg" and "10mg Tirzepatide (Mounjaro) 10mg" offered by www.usapeptide.com.
Coded names
A common response to enforcement has been to rename products: "GLP-1 S", "GLP-2 T", "GLP-3 RT", "GLP1-R". The letters simply list the code and the substance together, as in "GLP-1 S (Semaglutide)," "GLP-2 T (Tirzepatide)," "GLP-3 Reta (Retatrutide)"
in the August 2026 letter to Peptide Partners LLC. A name chosen so that buyers will recognise an approved medicine is evidence of what the buyer is expected to want it for.
The solvent sold alongside
Nine of the ten 2026 letters reviewed for this article name bacteriostatic water, under various product names, and reach the same conclusion about it:
Your firm offers "Bacteriostatic Water" for sale alongside peptide products, which are drugs intended for injection and require reconstitution, including the above-mentioned products. The sale of these products together demonstrates that you intend for your "Bacteriostatic Water" to be used in combination for injection. Therefore, your "Bacteriostatic Water" is a drug.
The significance is easy to miss. The agency did not merely count the solvent as supporting evidence about the peptides. It found that the solvent itself became a drug, because of what it was sold alongside. Selling things together is a circumstance of distribution, and under 21 CFR 201.128 circumstances are evidence.
The for injection
designation
The product names matter, and they are easy to misread. Bacteriostatic Water for Injection
is the name of a compendial (USP) article and of products marketed under approved drug applications, labeled for diluting or dissolving drugs for injection
. A solvent sold under that name states that use on its own label. One of the nine letters concerned a product sold under exactly that name.
The other eight did not use the designation. Their solvents were sold as Bacteriostatic Water
, Bac water
, BAC water
, Bacteriostatic Water 0.9% Benzyl Alcohol (10 ml)
, Bacteriostatic water for Peptides (BAC Water)
and Reconstitution Solution (BAC)
. FDA reached the same conclusion about every one of them. Leaving for injection
off the name did not change the outcome, because the agency's reasoning did not start with the solvent's name. It started with the peptides: having found them to be drugs intended for injection
, it concluded that a solvent offered alongside them was intended to be used with them in the same way. Names such as for Peptides
and Reconstitution Solution
only made the connection more explicit.
Two cautions follow. First, the designation cuts one way only: including for injection
states that use outright, but omitting it is no defence when everything around the solvent points the same way. Second, these findings are tied to their facts. Each letter concerns a solvent sold beside peptides that FDA had already found to be drugs intended for use in people; the letters do not say how the agency would regard a solvent supplied in a different context, and they do not commit it to any view. That, too, is FDA's interpretation in these cases, and it may be refined or extended.
Kits, calculators and guides
Where a seller offered the means of preparation or use, the letters said so explicitly. One kit paired a solvent with a syringe:
The sale of a kit containing the "BAC water" and a means of injection (a syringe) with these peptide drugs demonstrates that you intend for the "BAC water" to be used in combination for injection.
Two August 2026 letters went further, citing website tools:
In addition to the cited drug claims, you market bacteriostatic water alongside a "peptide guide" and "peptide calculator," resources that collectively provide the means to prepare an injectable drug for human administration.
Category text for known drug substances
Perhaps the most instructive quotations are the mildest. Alongside its stronger findings, the Royal Peptides letter quoted product text that reads, on its face, as cautious research language:
Semaglutide Single Vials is categorized under metabolic signaling research. It may be examined in research involving metabolic signaling, receptor selectivity and related biochemical pathways.
Tesamorelin is categorized under growth-signaling research. It may be examined in research involving peptide signaling, endocrine pathways and growth-hormone-related mechanisms.
These sentences were not the whole case. But their presence shows how the evidence is read: as a whole, in context, with every page of the site contributing to the picture. Language that might be unremarkable on a site with nothing else to say can become part of a pattern on a site that says a great deal.
The whole picture
No single item in the table above is the trigger. What the letters describe is a convergence: the choice of products, the names they are given, the words used about them, what is sold beside them and what tools are offered with them. Each element is ordinary on its own. Together they show what the business is for.
Intended use is not found in a sentence. It is found in the sum of a business.
That is also why enforcement tends to cluster around the same products. The substances named in the ten 2026 letters reviewed here include semaglutide, tirzepatide, retatrutide, survodutide, mazdutide, cagrilintide, SS-31, PT-141, tesamorelin and gonadorelin: for the most part, substances best known as approved medicines or as medicine candidates, for which consumer demand is overwhelmingly demand for use in people.
What follows a warning letter
A warning letter is FDA's notice that it considers a firm to be in violation. By the agency's own description it is informal and advisory, and it is not a final agency action: the firm can respond, contest the findings or correct them, and only a court can finally decide whether the law was broken. It is nonetheless the start of a record. Each of the 2026 letters asks for a written response within fifteen business days, setting out the corrections made and the steps taken to prevent recurrence, and warns that failure to correct may lead to further action without notice, including, without limitation, seizure and injunction
.
Other tools run in parallel. Import Alert 66-41 allows FDA to detain shipments of unapproved new drugs promoted in the United States without physical examination. A separate import alert, 66-80, restricts GLP-1 active ingredients to a "green list" of manufacturers whose facilities appear to comply with current good manufacturing practice. And where the evidence supports it, cases are referred for prosecution, as the July 2026 sentencing of the operators of an Indiana peptide business shows.
Frequently asked questions
- Does FDA need to buy or test a product before issuing a warning letter?
- Not in these cases. The 2026 letters describe reviews of the sellers' websites and rely on the text and offerings found there.
- If a site removes its claims, is the problem solved?
- Not necessarily. The letters show that product selection, names, accompanying items, tools and research-framed language can all contribute to intended use. Removing the most obvious sentences leaves the rest of the picture in place.
- Are research-language descriptions safe?
- Language that describes effects on the body remains a description of effects on the body, whatever verb introduces it. The letters quote "studied for" and "investigated for" statements, and even category text, as evidence.
- Why do the same substances keep appearing?
- Because intended use is judged in context. For substances best known as medicines, and widely sought for use in people, the surrounding evidence is more likely to point that way.
- Does a solvent become a drug only if it is labeled
for injection
? - No. Only one of the nine solvents named in the 2026 letters carried that designation. FDA reached the same conclusion about the others because they were offered alongside peptides it had found to be drugs intended for use in people. The designation states that use outright; leaving it off does not remove a use that the rest of the evidence shows.
- Will FDA always read the evidence this way?
- Not necessarily. These letters show FDA's current interpretation applied to particular websites. The agency's reading of the Act and its regulations, its priorities and the regulations themselves can change, and courts have the final word.
- Are all of FDA's actions published?
- No. FDA's compliance office describes advisory notifications that are not necessarily posted. The public letters are a minimum, not a complete count.
Sources & Further Reading
- Federal Food, Drug, and Cosmetic Act §§ 201(g)(1), 201(p), 301(d), 505(a); 21 U.S.C. §§ 321(g)(1), 321(p), 331(d), 355(a).
- 21 CFR 201.128, Meaning of "intended uses".
- Food and Drug Administration, Center for Drug Evaluation and Research, Office of Compliance. Annual Report 2025. April 2026.
- Food and Drug Administration. FDA launches agency-wide AI tool to optimize performance for the American people. Press announcement, June 2, 2025.
- Food and Drug Administration. Warning letter to USApeptide.com, reference 696885. February 26, 2025.
- Food and Drug Administration, CDER. Warning letter to Gram Peptides, reference 721806. March 31, 2026.
- Food and Drug Administration, CDER. Warning letter to Lovega LLC dba Pink Pony Peptides, reference 721088. March 31, 2026.
- Food and Drug Administration, CDER. Warning letter to PekCura Labs, reference 721709. March 31, 2026.
- Food and Drug Administration, CDER. Warning letter to Prime Sciences, reference 721805. March 31, 2026.
- Food and Drug Administration, CDER. Warning letter to Wholesale Peptide, reference 729447. June 17, 2026.
- Food and Drug Administration, CDER. Warning letter to NuScience Peptides LLC, reference 733652. August 24, 2026.
- Food and Drug Administration, CDER. Warning letter to Royal Peptides LLC, reference 734884. August 24, 2026.
- Food and Drug Administration, CDER. Warning letter to Peak Performance Peptides, reference 735127. August 24, 2026.
- Food and Drug Administration, CDER. Warning letter to Peptide Partners LLC, reference 735063. August 24, 2026.
- Food and Drug Administration, CDER. Warning letter to TXP Innovations LLC dba Tex Peptides, reference 735067. August 24, 2026.
- Food and Drug Administration. Import Alert 66-41: Detention without physical examination of unapproved new drugs promoted in the U.S.
- Food and Drug Administration. Import Alert 66-80: GLP-1 receptor agonist active pharmaceutical ingredients (green list).
- United States Attorney's Office, Northern District of Indiana. United States v. Matthew Kawa; sentencing of July 30, 2026.
- Food and Drug Administration. Regulatory Procedures Manual, Chapter 4: Advisory Actions (Warning Letters and Untitled Letters).
See also
For in vitro laboratory research only. Not for human or veterinary use. This library describes chemistry, analytical methods and published laboratory research; it gives no guidance on use in people or animals.