FDA Warning Letters to Peptide Sellers: What FDA Has Cited, 2023 to 2026

FDA sent at least 19 warning letters to online peptide sellers between June 2023 and August 2026. Most were about GLP-1 drugs such as semaglutide, tirzepatide and the unapproved retatrutide, often sold under code names. We found only one seller letter on FDA’s public index that names BPC-157 or TB-500, from June 2023.^[2] The charge is nearly always the same: an unapproved new drug, and a “research use only” label that FDA said did not change what the product was for. The HHS policy of October 28, 2026 covers 503A compounding pharmacies, not these sellers.^[1]

The letters FDA has sent to peptide sellers

The table lists every warning letter to an online peptide seller that we could find on fda.gov as of October 30, 2026. Of these, 17 are in our FDA warning letter register, which follows GLP-1 drugs and links each one to its own page. The other 2 name no GLP-1 drug, so the register does not carry them; they are cited to FDA directly. The letters came in batches: 2 on February 7, 2024, 4 on December 10, 2024, 5 on March 31, 2026, 5 on August 24, 2026.

Two patterns stand out. GLP-1 copies dominate: semaglutide, tirzepatide and retatrutide appear in almost every row, often relabeled “GLP-1 SM” or “GLP-3 RT”.^[9] The sellers FDA wrote to in August 2026 had moved on to SS-31, PT-141 and tesamorelin as well.^[5][6] Our page on retatrutide and the gray market covers why that drug in particular is sold this way.

Searches for a November 2025 peptide letter usually lead to a December 12, 2025 letter to Pinnacle Professional Research, which does business as Pinnacle Peptides. FDA reviewed its website in November 2025, but the products it cited were SARMs (selective androgen receptor modulators), not peptides, so it is left out of the table. They were sold under “FOR RESEARCH ONLY” and “NOT FOR HUMAN USE” labels.^[12] We found no warning letter to a peptide seller dated November 2025.

What FDA has said about BPC-157, TB-500 and other non-GLP-1 peptides

Despite how widely they are sold, the healing peptides appear in very few letters. The June 12, 2023 letter to Warrior Labz SARMS is the only seller letter we found on FDA’s index that names BPC-157 or TB-500. FDA listed both as injectable and nasal-spray products and quoted the site’s claims about gut healing, ulcers and wound repair, along with a weekly injection schedule.^[2] It called both unapproved new drugs and added a footnote warning that intranasal products can cause bleeding, ulceration or a perforated nasal septum when the contents are toxic.^[2]

Compounders have been cited too. A November 10, 2021 letter to an Indianapolis compounder, the Guyer Institute of Molecular Medicine, said it had compounded with substances that were not on the 503A bulks list. A footnote spelled out that “thymosin beta, BPC-157, LL-37, pentosan, Selank, and Semax were not nominated” for the list at that time.^[3] On January 20, 2026 FDA wrote to GenoGenix LLC, a 503B outsourcing facility in Florida. It called that facility’s thymosin beta-4 both an unapproved new drug and a biological product that needs a biologics license, and listed its epithalon among products whose labels lacked the words “this is a compounded drug.”^[4] The firm had stopped production and recalled its sterile products.^[4]

Other letters name peptides sold on the same sites: thymalin in February 2024, and Prostamax and gonadorelin in June 2026.^[14][13] FDA’s safety-risk page now lists both among substances whose nominations were withdrawn, but it keeps its earlier assessment: FDA has “not identified any human exposure data” for the TB-500 fragment, and only limited safety information for BPC-157.^[16] What FDA has published on BPC-157 is covered in BPC-157: what FDA actually said, and the TB-500 profile is at TB-500.

What the letters cite

The letters are short and follow a template. Each one applies the same handful of legal points, and they explain most of what happens in this market.

• Unapproved new drug. Every seller letter in the table says the products are “new drugs” with no approved application, so shipping them across state lines breaks sections 505(a) and 301(d) of the Food, Drug, and Cosmetic Act.^[5][10]
• Intended use beats the label. Each of the 17 register letters quotes the seller’s research-only or not-for-human-use disclaimer and then sets it aside, because claims on the website showed the products were meant for people.^{[10][8][14][15]}
• Research wording counts as a claim. In August 2026 FDA quoted product pages that spoke only of “preclinical models” and still treated them as evidence of human drug use.^[5]
• Mixing supplies are evidence. Bacteriostatic water, reconstitution kits with syringes and online “peptide calculators” were cited as proof the seller expected the vials to be injected. Several letters list the water itself among the unapproved drugs.^[8][6][7][5]
• Misbranding. Where FDA charged it, the point was that prescription drugs sold to the public cannot carry adequate directions for a layperson, and that selling them without a prescription misbrands them.^[11][4]

“Despite statements on your product labeling marketing your products for ‘research use only’ and ‘not for human consumption,’ evidence obtained from your website establishes that your products are intended to be drugs for human use.”

— FDA warning letter 735127, August 24, 2026

An approved version of a molecule does not help the seller. In a February 2025 letter FDA noted that FDA-approved semaglutide exists, then said no approved application covered the vials that seller offered.^[11] The same logic applies to PT-141 and tesamorelin vials on research sites. Which peptides do have approved products is set out in FDA-approved peptides.

Each seller letter asks for a written reply within 15 working days (the August 2026 letters say business days) and warns that failure to fix the violations “may lead to regulatory or legal action including, without limitation, seizure and injunction.”^[12][5] A letter is a warning. Whether a seller kept selling afterward is not something the letter itself can tell you.

What the October 28, 2026 HHS policy changes for these sellers

For research-chemical sellers, nothing. HHS said it “does not intend to take enforcement action against a State-licensed pharmacy, Federal facility, or licensed physician” compounding six peptides under section 503A: BPC-157, TB-500, epitalon, Semax, KPV and MOTS-c.^[1] An online shop selling vials labeled for research is none of those. HHS gave its reason in the same document. The policy is meant to “discourage the continued, widespread use of certain research-use-only peptides supplied by foreign manufacturers that pose a safety risk to US patients.”^[1]

Even a licensed pharmacy gets the cover only under ten conditions. The drug must contain a single listed peptide, use the routes the policy covers, be made from a substance sourced from an FDA-registered facility with a valid certificate of analysis, be compounded against a patient-specific prescription, and carry the label “This is a compounded drug product. Not for resale.”^[1] Research sites fail most of those by design: they sell blends, sell without a prescription, and say the product is not for people. The full list is in our explainer on the HHS peptide compounding policy.

The policy is also temporary. It lasts until each peptide is settled in a final rule on the 503A list, and HHS says it may revisit the policy “if, among other things, a safety signal or product quality issue arises.”^[1] FDA’s warning letters to research sites rest on the drug-approval law, which the policy does not touch. The difference between a vial from a research site and a compounded prescription is the subject of research-use-only versus compounded peptides, and where each peptide stands legally is in are peptides legal?

What this means if you are buying peptides

A “research use only” label is the line FDA has quoted back to sellers in letter after letter. It does not make the vial legal, and it does not tell you what is in it. FDA’s concern in the BPC-157 review was identity and impurities, which a seller’s own certificate cannot settle.^[16] If you want one of the six peptides now covered, the route HHS describes is a prescriber and a 503A pharmacy, with a single-ingredient product and the compounded-drug label. That is still an unapproved drug, and no dose of it is approved. You can check any company’s record on our FDA warning letter pages.