Who decides what a product is for?

A supplier that takes compliance seriously has to understand not only the rules, but how they are applied. This piece looks at how "intended use" is actually decided in research-use-only cases. Most of it is fact, drawn from the statute, the regulations, FDA's own documents and the courts. The questions at the end are ours.

A standard without a threshold

Whether a substance is a drug turns on its intended use, and intended use is a matter of inference. FDA's regulation, 21 CFR 201.128, says intent may be shown by a seller's expressions, the design or composition of the product and the circumstances of its distribution. When FDA revised the regulation in 2021, it described the evidence it may consider in the broadest terms:

the Agency may look to any relevant source of evidence, including a variety of direct and circumstantial evidence

What the regulation does not contain is a threshold. There is no list of what is sufficient, no statement of how different kinds of evidence are weighed against each other, and no description of evidence that would count against a finding of human intended use. The standard is open by design.

A case built by arrangement

Warning letters show how that open standard is applied. A typical letter quotes passages from different pages of a website, one after another: a product description, a comparison article, a category line, a kit listing, a footnote about a solvent sold elsewhere on the site. The conclusion that the products are drugs follows the quotations.

Read individually, the quoted passages vary widely. Some are plain claims about the body. Others are cautious, research-framed category text that would be unremarkable on its own. The letters do not say which passages were necessary to the conclusion, whether the milder ones would have mattered without the stronger ones, or what, if anything, the seller could have shown that would have pointed the other way.

When a case is assembled from many sources, each new item can be read as confirming the picture. It is fair to ask what would ever count against it.

Reviewer, author and publisher

In these cases, the same agency reviews the website, interprets what it finds, writes the letter and publishes it. The letters to peptide sellers issued in June and August 2026 each close the same way:

Please note FDA posts warning letters on www.fda.gov.

The recipient is asked to respond within fifteen working or business days, to the agency that wrote the letter. There is no hearing before publication, and no independent reviewer between the agency's reading of a website and the public record of that reading.

Published, but not reviewable

FDA describes the status of a warning letter carefully:

A Warning Letter is informal and advisory. It communicates the agency's position on a matter, but it does not commit FDA to taking enforcement action. For these reasons, FDA does not consider Warning Letters to be final agency action on which it can be sued.

The courts have agreed. In Holistic Candlers and Consumers Association v. FDA (2012), the D.C. Circuit held that warning letters are not final agency action and so cannot be challenged under the Administrative Procedure Act.

Both things are true at once. A warning letter is informal, advisory and not open to judicial review. It is also a public document, under the agency's name, stating that a named business is selling unapproved new drugs. Customers, suppliers, payment providers and platforms can read it and act on it. Unless the agency takes a further step that a court can examine, the business has no forum in which to contest the finding.

The legal ground is shifting

The legal landscape around agency interpretation has changed in recent years:

• In Loper Bright Enterprises v. Raimondo (2024), the Supreme Court overruled the Chevron doctrine. Courts no longer defer to an agency's reading of an ambiguous statute; they must decide what the law means for themselves.
• In Whitaker v. Thompson (2004), the D.C. Circuit held that the First Amendment allows FDA to use speech as evidence of intended use.
• In United States v. Caronia (2012) and Amarin Pharma v. FDA (2015), courts held that truthful, non-misleading speech about the unapproved uses of approved drugs is protected, and cannot by itself be the basis of a misbranding case.

None of these cases concerned research-use-only suppliers. Together, though, they leave open questions that matter to them. How far can accurate descriptions of published science be used as evidence of intent? How much evidence, and of what kind, is enough? And when an agency's interpretation is expressed only in documents that courts will not review, when does a court get to look at it at all?

What clarity could look like

In our view, everyone in this area, including regulators, would benefit from clearer rules. Clarity could take several forms:

• Published criteria. Guidance, developed with public comment, on what FDA regards as evidence of human intended use for research materials, and how it weighs that evidence.
• Evidence that counts both ways. Recognition that documented buyer qualification, recorded research-use agreements and refusal of use enquiries are evidence too, and weigh against a finding of human intended use.
• A chance to answer first. An opportunity to respond to the agency's reading before it becomes a public record.
• Consistency. Similar evidence weighed the same way, so that compliant suppliers can know where they stand.

The law provides channels for questions like these: citizen petitions under 21 CFR 10.30, public comment on guidance under FDA's good guidance practices in 21 CFR 10.115, and, when a case reaches them, the courts. Questions of this kind are usually raised collectively, and they carry most weight when they come from those with the most to gain from clear rules: the suppliers trying to follow them.

Where we stand

We believe that a standard which can be met with certainty is better for researchers, for suppliers and for the public than one that can only be inferred from the letters it produces. Clear rules reward those who follow them, and they make the agency's own work more consistent. That is the kind of system we would like to see, and the kind we are prepared to argue for, through the channels the law provides.

Sources & Further Reading

1. Federal Food, Drug, and Cosmetic Act § 201(g)(1); 21 U.S.C. § 321(g)(1).
2. 21 CFR 201.128, Meaning of "intended uses".
3. Food and Drug Administration. Regulations regarding "intended uses". Final rule. Federal Register 2021;86:41383. August 2, 2021.
4. Food and Drug Administration. Regulatory Procedures Manual, Chapter 4: Advisory Actions (Warning Letters and Untitled Letters).
5. Food and Drug Administration, CDER. Warning letters to online peptide sellers dated March 31, 2026 and August 24, 2026, including reference 734884.
6. Holistic Candlers and Consumers Association v. Food and Drug Administration, 664 F.3d 940 (D.C. Cir. 2012).
7. Loper Bright Enterprises v. Raimondo, 603 U.S. 369 (2024).
8. Whitaker v. Thompson, 353 F.3d 947 (D.C. Cir. 2004).
9. United States v. Caronia, 703 F.3d 149 (2d Cir. 2012).
10. Amarin Pharma, Inc. v. Food and Drug Administration, 119 F. Supp. 3d 196 (S.D.N.Y. 2015).
11. 21 CFR 10.30, Citizen petition.
12. 21 CFR 10.115, Good guidance practices.