Quick answer: the FDA warning letters sent to peptide sellers from 2024 to 2026 follow one pattern. FDA says the products are unapproved new drugs under FD&C Act sections 505(a) and 301(d), and often misbranded, and it rejects “research use only” labels when the website shows human use.[1] We verified at least 13 letters to research-peptide sellers in that period, plus at least 30 letters to telehealth companies over compounded GLP-1 marketing.[7]
This page analyzes the letters by type, with dates and examples from FDA’s public database. Companies are named only because the letters are public enforcement records; we do not link their websites. For background, see research use only peptides, the FDA peptide compounding crackdown, and our FDA & Regulation hub.
What an FDA warning letter is
A warning letter is FDA’s formal notice that it believes a company is violating federal law. It is not a court ruling. The company usually has 15 working days to explain how it will fix the problems, and the letters say that failure to do so may lead to seizure or injunction.[4][10]
Peptide letters come from two parts of FDA’s drug center:
- Office of Unapproved Drugs and Labeling Compliance: online sellers of “research” peptides.
- Office of Compounding Quality and Compliance: compounders, ingredient suppliers and telehealth marketers of compounded drugs.[8]
Letters to “research use only” peptide sellers
These are the letters most readers ask about. The ones we verified on fda.gov:
| Letter date | Recipients | Peptides named |
|---|---|---|
| Feb 7, 2024 | Synthetix Inc. dba Helix Chemical Supply | Semaglutide, tirzepatide |
| Dec 10, 2024 | Summit Research Peptides, Xcel Research, Swisschems, Prime Vitality dba Prime Peptides | Semaglutide, tirzepatide, retatrutide, cagrilintide, mazdutide |
| Mar 31, 2026 | Gram Peptides, Lovega LLC dba Pink Pony Peptides, Prime Sciences | Retatrutide (including under code names like “GLP-3 RT”), tirzepatide, semaglutide, cagrilintide, mazdutide, bacteriostatic water |
| Aug 24, 2026 | Royal Peptides, Peptide Partners, Peak Performance Peptides, NuScience Peptides, TXP Innovations dba Tex Peptides | Retatrutide, semaglutide, tirzepatide, tesamorelin, SS-31, PT-141 |
Sources: the individual letters and FDA’s December 2024 roundup.[2][3][4][9][10][11][14][15] FDA’s consumer page adds that it has also warned sellers of survodutide labeled “for research purposes” or “not for human consumption.”[1]
The trend is clear: early letters focused on copies of approved GLP-1s; 2026 letters reached investigational drugs like retatrutide and non-GLP-1 peptides like tesamorelin and SS-31.
Why “research use only” labels fail
Under FDA regulations, a product’s intended use is judged by objective intent, which includes how it is advertised and sold, not just the label.[12] The letters apply this directly:
- Website claims. The Gram Peptides letter cited claims about appetite suppression, weight reduction and blood sugar.[9]
- Reconstitution supplies. The Royal Peptides letter said selling bacteriostatic water with a “peptide guide” and “peptide calculator” provided the means to prepare an injectable drug for people.[10]
- Social media. The Summit letter relied on product pages and social posts describing weight loss and diabetes uses.[4]
FDA also stresses that injectables bypass some of the body’s “key defenses against toxins and microorganisms.”[10]
Letters to compounders and ingredient suppliers
A second group targets the supply chain behind compounded peptides.
- Compounded retatrutide. The September 9, 2025 letter to ASN-LABS called its compounded retatrutide an unapproved new drug and misbranded under 502(f)(1), and cited false or misleading claims about compounded semaglutide under 502(bb).[5]
- Ingredient importers. The December 8, 2025 letter to Darmerica cited manufacturing (CGMP) violations and said it supplied retatrutide to pharmacies compounding under 503A, though retatrutide is “not eligible for use in compounding under section 503A.” FDA also noted shipments labeled “custom peptide” without the drug name. The firm told FDA it had stopped distributing retatrutide.[6]
The Darmerica letter also lists other active ingredients it considers ineligible for 503A compounding, including cagrilintide, elamipretide (SS-31) and thymogen.[6] For how 503A and 503B differ, see 503A vs 503B compounding.
Letters about compounded GLP-1 marketing
The largest wave is about advertising, not unapproved ingredients. FDA began a crackdown on misleading drug ads in September 2025, and on March 3, 2026 announced 30 warning letters to telehealth companies.[7] The main violations:
- Claims implying a compounded drug is the same as an approved one, such as “same active ingredient” as a brand.
- Branding that implies the telehealth company is the compounder.
The February 20, 2026 letter to Better Health Labs (Measured) is typical. It cited “same active ingredient” claims and called the products misbranded under 502(a) and 502(bb).[8] More detail is in our guide to peptide advertising rules.
Common violations at a glance
| Violation | FD&C Act section | Typical trigger |
|---|---|---|
| Unapproved new drug | 505(a), 301(d) | Selling a peptide for human use with no approved application |
| Misbranding: no adequate directions | 502(f)(1) | Drug for an unapproved use cannot carry adequate directions |
| Misbranding: false or misleading | 502(a), 502(bb) | “Same as” or “FDA-approved” claims for compounded products |
| Adulteration (CGMP) | 501(a)(2)(B) | Poor quality control by ingredient suppliers |
Five patterns across 2024–2026
Reading the letters side by side, a few trends stand out:
- Batches, not one-offs. FDA tends to post letters in groups on the same day, such as four GLP-1 sellers in December 2024 and five peptide sellers on August 24, 2026.[3][10]
- Code names do not help. Sellers listed retatrutide as “GLP-3 RT” or “GLP1-R,” and FDA still identified and cited the drug.[14][15]
- The scope is widening. Letters moved from copies of approved GLP-1s to investigational drugs (retatrutide, mazdutide, cagrilintide) and then to non-GLP-1 peptides like tesamorelin, SS-31 and PT-141.[11]
- Supplies count as evidence. Bacteriostatic water, reconstitution kits and dose calculators appear repeatedly as proof of intended injection.[9][10]
- The supply chain is a target. FDA now writes to the ingredient importers that feed compounders, not just the sellers patients see.[6]
What the letters mean for patients
The letters are about sellers, not buyers, and FDA does not test the products before writing them. Still, they tell patients three useful things. First, if a peptide’s website offers dosing advice next to a “not for human use” label, FDA considers that a drug sold without approval. Second, a compounded GLP-1 advertised as the “same” as a brand-name drug is being marketed in a way FDA calls misleading. Third, FDA has collected 990 adverse event reports for compounded semaglutide and more than 730 for compounded tirzepatide as of May 31, 2026, which is part of why it is pressing on the supply chain.[1]
What happens after a letter
Most letters end with corrections or with the company leaving the market. Some lead to court. In one older case, a Kentucky compounding pharmacy pleaded guilty in October 2020 to distributing unapproved drugs. Its plea listed BPC-157, Semax, epitalon and other peptides, and it forfeited about $1.79 million.[13]
To check a company, search FDA’s warning letter database by name or by compound. Absence of a letter does not mean a seller is compliant.
This is general information, not legal advice. For the wider timeline, see FDA peptide regulation timeline.
