FDA sends warning letters to five online peptide sellers

The Food and Drug Administration posted five warning letters dated August 24, 2026 to companies selling injectable peptides online. Each letter says FDA reviewed the company’s website in July 2026 and concluded that the products listed are unapproved new drugs under section 505(a) of the Federal Food, Drug, and Cosmetic Act.

Who received letters, and for what

The disclaimer did not decide it

Every letter makes the same legal move. A product is a “drug” under section 201(g)(1) if it is intended to diagnose, treat or prevent disease, or to affect the structure or function of the body. FDA judges intended use from the seller’s own labeling and marketing (21 CFR 201.128), not only from the warning on the vial.

In the Peptide Partners letter, FDA quotes product-page text describing study findings, such as semaglutide having “a protective effect on brain cells” and retatrutide’s “powerful effects on weight loss and blood sugar control.” A footnote states that despite “for research use only” and “not for human or veterinary use” statements, “evidence obtained from your website establishes that your products are intended to be drugs for human use.”

Why bacteriostatic water was named

Four of the five letters list bacteriostatic (BAC) water. FDA’s reasoning in the Peptide Partners letter is that the company “offers ‘Reconstitution Solution (BAC)’ for sale to be used to reconstitute the peptide products,” and “the sale of these products together demonstrates that you intend” it to be used for injection, which makes it a drug too. The same footnote says that by marketing BAC water as a solvent the seller was “providing the means to prepare an injectable drug for human administration.”

What a warning letter is, and is not

A warning letter is FDA’s notice that it believes the law is being broken. It asks for a written response, here within 15 business days, and warns that failure to correct violations “may result in regulatory or legal action without further notice including, without limitation, seizure and injunction.” It is not a court ruling or a penalty in itself. FDA’s posted pages do not show whether the companies responded. We checked each website on October 19, 2026; the results are on each company’s status log.

Pattern

These letters continue a run that includes December 2024 letters to research-chemical sellers of semaglutide and retatrutide (report) and March 31, 2026 letters to Gram Peptides and Prime Sciences (report). The August batch is the first in our tracker to add SS-31, PT-141 and tesamorelin products to the list.