What FDA's 2026 peptide warning letters cite, sentence by sentence

FDA issued twelve warning letters to online peptide sellers in 2026: seven dated 31 March and posted 7 April, five dated 24 August and posted 1 September. Read side by side, they are one letter written twelve times. Each recites the seller's research-use-only disclaimer and sets it aside in a single sentence. Each reaches the drug definition through the seller's own website. Three of the March letters and all five of the August letters name bacteriostatic water as an unapproved drug in its own right. Two cite a peptide calculator or guide as evidence of what the products are for. And every product list places the storefront's coded name next to the compound it stands for. This piece quotes the agency's sentences, not the sellers', and the interactive readers below let you check each one against the letter it came from.

Which sentence disposes of the disclaimer?

The same one, every time, varying only in the disclaimer it quotes back. To Gram Peptides on 31 March: "Despite statements on your product labeling marketing your products for 'Research Use Only,' and 'not intended for human consumption, medical use, or veterinary use,' evidence obtained from your website establishes that your products are intended to be drugs for human use." To Prime Sciences the same day, the disclaimer was "laboratory research purposes only." To NuScience Peptides on 24 August it was "for laboratory, research, and analytical use." The sentence around those quotations does not change.

What the construction does is worth stating exactly. FDA does not argue that the disclaimer is false, and it does not argue that the phrase is meaningless. It acknowledges the disclaimer and then says the website establishes a different intent. That is the intended-use rule at 21 CFR 201.128 applied as written: intent is objective, it is shown by labeling claims and advertising matter, and one statement does not settle it against the rest of the record. A disclaimer that sits above copy pointing the other way is outweighed, not overruled.

How do the letters define a drug?

Through both prongs of section 201(g)(1). The Gram Peptides letter puts it in one sentence: "Your products are drugs as defined by section 201(g)(1) of the FD&C Act because they are intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease and/or intended to affect the structure or function of the body." The "and/or" matters. The second prong, structure or function, does not need a disease to be named. Copy describing what a compound does in a body qualifies on its own.

The Prime Sciences letter then shows where the evidence came from. It introduces the quoted copy with: "Examples from your product labeling, including on your website, that provide evidence of the intended use (as defined in 21 CFR 201.128) of these products as drugs include". Two things sit inside that sentence. The website is called labeling. And the regulation cited is the objective-intent rule, so the copy is being read for what it objectively conveys, not for what the seller says it meant.

The copy FDA quoted is not reproduced here. It is in the letters, which are public, and restating it would be restating the language the agency treats as evidence.

Why is bacteriostatic water in the letters at all?

Because FDA treats it as evidence of what the peptides are for, and then as a drug itself. In the Gram Peptides letter, FDA notes that the firm sells its bacteriostatic water alongside the peptide products, including the two GLP products named earlier, and reads the solvent as showing those peptides are meant to be prepared and given to people. Two sentences later it concludes that the water is therefore a drug in its own right. NuScience, five months on, gets the same reasoning: FDA describes its "Bacteriostatic water for Peptides (BAC Water)" as sold for use with the peptides on its website, which the agency treats as drugs for human use.

The logic is combinational. A solvent sold next to a compound tells the agency how the compound is meant to be used. Once that is established, the solvent is offered "in combination" with a drug and is charged as one. In the August batch this appears in all five letters. It is the clearest example of a principle that runs through the whole series: the composition of a storefront is evidence, independent of any sentence written about a compound.

What about calculators and kits?

They are cited as evidence on their own terms. In the Prime Sciences letter, FDA finds that a kit bundling the "BAC water" and a syringe with the peptides shows the firm intends the solvent to be used with those peptides in people. The NuScience letter goes further and reaches tooling with no physical product attached: it cites a "peptide calculator", marketed alongside bacteriostatic water, as a resource for preparing the peptides as a drug for people.

That second point is the one with consequences for anyone publishing content about research peptides. A preparation calculator makes no claim about any compound. FDA cited it anyway, because a tool for preparing a compound for use in people is a statement about what the material is for. The same reasoning reaches dose tables, preparation instructions and syringe-unit conversions wherever they appear on a site.

Did renaming the products help?

No. Every letter lists the products FDA is calling unapproved new drugs, and the lists pair the storefront's label with the compound. Gram Peptides is listed for Retatrutide (sold as its "GLP-1-R peptide"), Tirzepatide (sold as its "GLP-2 peptide") and its bacteriostatic water. Prime Sciences: "Cagrilintide, GLP1-R, GLP1-S, GLP1-T, Mazdutide, and BAC water". NuScience: "GLP-2 Tirz Peptide, GLP-1 Sema Research Peptide, GLP-3 RT (Retatrutide) Research Peptide, Survodutide, Mazdutide, PT-141 Peptide (Bremelanotide), Tesamorelin Research Peptide, Tesamorelin Ipamorelin Blend, Bacteriostatic water for Peptides (BAC Water)".

Across the three letters read in full, retatrutide, tirzepatide and bacteriostatic water appear in all three. Coded names were listed as written and treated as the drug they denote. The word "Research" inside a product name was listed along with the rest.

What does a letter demand, and what does it not decide?

Each letter gives the same clock. March: "Please notify FDA in writing, within fifteen working days of receipt of this letter, of the specific steps you have taken to correct any violations." August: "Send your written response to FDAAdvisory@fda.hhs.gov within fifteen (15) business days of receipt of this letter."

A warning letter is the agency's position, not a court's. None of the twelve has been adjudicated, and none alleges a product-quality failure: no contamination, subpotency or misidentification is asserted in the letters read for this piece. The theory is intended use as shown by marketing, and the record used to prove it is the seller's own site.

What the twelve letters establish, together

Five things, each stated in FDA's own sentences above. A research-use-only disclaimer is acknowledged and outweighed, whatever its wording. Website copy is labeling, and the structure-or-function prong means it need not mention a disease. Bacteriostatic water sold alongside compounds is both evidence and, itself, an unapproved drug. Calculators, guides and kits are evidence without any claim attached to them. And a renamed product is listed beside its real name.

Veridian Research supplies material for in-vitro laboratory research only. This piece is a reading of public regulatory documents, not legal advice, and the citations are given so each sentence can be checked against its source.

Sources

FDA warning letters, all in the agency's public database by reference number: Gram Peptides, MARCS-CMS 721806, 31 March 2026. Prime Sciences, MARCS-CMS 721805, 31 March 2026. NuScience Peptides LLC, MARCS-CMS 733652, 24 August 2026. The remaining March recipients were Lovega LLC dba Pink Pony Peptides (721088), Mile High Compounds LLC (721600), PekCura Labs (721709), FormPour (722215) and Guangzhou Huli Technology dba Fantasy Face (722228). The remaining August recipients were TXP Innovations LLC dba Tex Peptides (735067), Royal Peptides LLC (734884), Peptide Partners LLC (735063) and Peak Performance Peptides (735127). 21 CFR 201.128 and 21 U.S.C. 321(g)(1) are quoted from the current text.