Few sellers set out to sell unapproved drugs. Most cross the line gradually, through decisions that each look reasonable on their own: a more descriptive product name, a helpful calculator, a solvent that customers keep asking for, an affiliate with a large audience. Because intended use is judged from the whole business, these decisions add up. This article sets out the mistakes that appear again and again in the public record, and why each one matters.
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. Where this article relies on FDA's letters, it describes how the agency has read the evidence so far.
Each mistake below connects to the same rule. Under 21 CFR 201.128, intended use may be shown by a seller's expressions, the design or composition of what it sells, the circumstances of distribution, and what it knows about how its products are used. Every item on this list is evidence under one of those headings.
Mistakes in what is said
1. Relying on the disclaimer
The disclaimer is the first thing FDA's letters quote, and the first thing they set aside. A research-use-only statement counts in a seller's favour only when everything else agrees with it. Placed on a site that says otherwise, it becomes evidence that the seller knew where the line was.
2. Translating claims into research language
Replacing "reduces appetite" with "studied for its effects on appetite" changes the grammar, not the claim. FDA has quoted "studied for", "investigated for" and "researched for" statements, and text about "preclinical models", as evidence of intended use. What matters is the effect being described, and whether it is an effect on the human body.
3. Borrowing the authority of approved medicines
Brand names in product titles, statements that a substance is FDA-approved, clinical trial results for approved products and comparisons with them all tell the reader what the product is for. FDA's letters cite all of these, and point out that an approval belongs to a specific product, not to every sample of the molecule.
4. Describing mechanisms in terms of the body
Science-heavy copy is not automatically compliant. A description of how a substance acts on appetite, hormones or metabolism in people is a description of its effects in people, however technical the vocabulary. Compliant scientific writing stays with chemistry, analytical data and published in vitro work.
Mistakes in what is sold
5. Coded product names
Renaming a product "GLP-2 T" or "GLP-3 R" does not hide it. FDA's letters list the code beside the substance. Worse, a code designed to be recognised as an approved medicine shows exactly whom the product is aimed at.
6. Selling the solvent beside the peptide
In nine of the ten 2026 letters reviewed for this series, bacteriostatic water was named, and in each FDA found that selling it alongside the peptides made the solvent itself a drug. Where a kit added a syringe, the letter called it a means of injection
. Accompanying products are circumstances of distribution, and they speak for the business.
The solvent's name was not the deciding factor. Only one of the nine was sold under the designation for Injection
, which states that use outright; FDA reached the same conclusion about the eight that were not, because of the peptides they were sold beside. Dropping a word from a product name does not change what the rest of the business shows. The second article in this series sets out the letters' reasoning in detail.
7. Calculators, guides and protocols
Preparation calculators and usage guides draw search traffic and keep customers on a site. They are also, in FDA's words, resources that provide the means to prepare
a product for use in people. Their usefulness to a buyer is precisely what makes them evidence.
8. Blends, stacks and outcome-named collections
Combining products, or grouping them into collections named after outcomes rather than chemistry, describes a purpose. A blend named for "body composition" or a collection headed "recovery" says what it is for more plainly than any single product page.
Mistakes in who speaks for the business
9. Affiliates, promoters and influencers
The regulation reaches statements by a seller's "representatives". A promoter paid in commission or discount codes, whose content describes use in people, is speaking for the business. Many of the most explicit statements about these products are made not on stores but in videos and posts that link to them.
10. Reviews and testimonials left standing
A review describing personal use, published on a product page, is content the seller chose to display. Left in place, it is both an expression of the business and evidence of what the business knows its customers are doing.
11. Social media and community groups
Posts, replies, stories and members-only groups are all expressions of the business. A compliant website does not offset a social account, a forum or a messaging group that says what the website does not.
Mistakes in whom the business serves
12. Selling to anyone
A seller that asks nothing of its buyers sells, by design, to whoever arrives. For products whose public demand is mostly demand for use in people, that is a circumstance of distribution that points one way. Knowing who the buyer is, and declining those who are not doing research, is part of what makes a research-use-only claim credible.
13. Answering use questions
"How much should I take?" is one of the most common questions sent to peptide sellers. Any answer other than a refusal is an oral or written statement of intended use. Even a refusal leaves the seller with knowledge of what the customer intends, and the regulation counts knowledge as evidence. The compliant response declines, records and, where the intent is clear, does not sell.
Mistakes in how the business runs
14. Documentation that does not match the vial
A certificate of analysis that belongs to another lot, or analytical claims that are not true, create a different problem: the product is not what its labeling says. In the Indiana case that ended in federal prison sentences in July 2026, investigators found that many products sold as containing one class of compound in fact contained testosterone.
15. Fixing the page, not the business
After a letter, the instinct is to delete the quoted sentences. FDA's letters ask for more than that:
As previously stated, you are responsible for investigating and determining the root causes of any violations and implementing corrective and preventative measures to ensure future and sustained compliance so that these violations and any others do not occur.
If the products, the names, the solvent, the calculator and the customer base are unchanged, the intended use is unchanged.
Mistakes in how risk is judged
16. Accepting enforcement as a cost of doing business
A warning letter can look like a manageable risk, set against the revenue of an unrestricted catalogue. That calculation leaves out the rest of the toolkit: seizure, injunction, import detention and criminal prosecution, under a statute that can hold responsible individuals liable without proof that they personally took part.
17. Assuming small means invisible
The recent letters are addressed to small online businesses, identified by reviewing their websites, often in sweeps of several firms on a single date. FDA describes ongoing online surveillance, and has deployed AI tools across the agency, including for compliance. Size is not cover.
The pattern behind the mistakes
Every mistake on this list makes commercial sense. Each one adds traffic, conversion, basket size or loyalty. That is why they are common, and why they are hard to give up: compliance is not a matter of avoiding obvious wrongdoing, but of declining a long series of individually profitable choices. The next article in this series looks at what that costs.
Frequently asked questions
- Is any one of these mistakes enough on its own?
- Intended use is judged from the whole picture, so the weight of any single item depends on everything else. The letters typically cite several categories of evidence together.
- Is selling a solvent illegal?
- The 2026 letters do not say that a solvent is a drug in every setting. In each of them it was the sale of the solvent beside peptides FDA had found to be drugs that led it to find the solvent was itself a drug, whether or not the solvent's name included
for Injection
. The letters express FDA's interpretation on those facts; they do not commit the agency to a view of other settings, and that interpretation may change. - Can a seller control what affiliates say?
- If it cannot, it should not have them. Statements by representatives are part of the evidence of intended use.
- What should a seller do when a customer reveals use in people?
- Decline to advise, record the exchange, and decline the sale. The regulation counts a seller's knowledge of how its products are used as evidence of intent.
Sources & Further Reading
- 21 CFR 201.128, Meaning of "intended uses".
- Federal Food, Drug, and Cosmetic Act §§ 201(g)(1), 201(p), 301, 303, 505(a); 21 U.S.C. §§ 321, 331, 333, 355.
- Food and Drug Administration, CDER. Warning letter to Gram Peptides, reference 721806. 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 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. Warning letter to USApeptide.com, reference 696885. February 26, 2025.
- Food and Drug Administration. FDA expands artificial intelligence capabilities with agentic AI deployment. Press announcement, December 1, 2025.
- United States Attorney's Office, Northern District of Indiana. United States v. Matthew Kawa; sentencing of July 30, 2026.
- United States v. Park, 421 U.S. 658 (1975).
- 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.