Peptency Academy · Research progress
FDA warning letters of 24 Aug 2026 on retatrutide, semaglutide and other peptides sold as research use only
Semaglutide, tirzepatide, retatrutide, SS-31, PT-141 and tesamorelin are among the products named in five FDA warning letters dated 24 Aug 2026, which state that research use only statements on online peptide sellers' labelling did not decide the products' status: evidence from the sellers' websites established that the products are intended to be drugs. Source sentence
Footnote 1 in each letter: 734884 "Despite statements on [the firm's] product labeling marketing [the firm's] products 'for research use only' ... evidence obtained from [the firm's] website establishes that [the firm's] products are intended to be drugs"; 735067 "'research use only', 'for research and laboratory use only'"; 735063 "'for research use only'"; 733652 "'for laboratory, research, and analytical use'"; 735127 "for 'research use only'"1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 20262 FDA warning letter 735067 (TXP Innovations LLC dba Tex Peptides), 24 August 20263 FDA warning letter 735063 (Peptide Partners LLC), 24 August 20264 FDA warning letter 733652 (NuScience Peptides LLC), 24 August 20265 FDA warning letter 735127 (Peak Performance Peptides), 24 August 2026 An FDA warning letter is a written notice that names violations of the Federal Food, Drug, and Cosmetic Act and asks the firm to respond in writing within 15 business days. Source sentence
"This warning letter advises [the firm] of significant violations observed during a U.S. Food and Drug Administration (FDA) review of [the firm's] website."; "Send [the firm's] written response to FDAAdvisory@fda.hhs.gov within fifteen (15) business days of receipt"1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 2026
Regulatory content shown for: United States and the Americas.
Research progressAcademy24 August 2026Regulator action
Did research use only labelling decide the products' status?
No. Each letter states that, despite research use only statements on the firm's product labelling, evidence from the firm's website establishes that the products are intended to be drugs, and the letters classify the named products as unapproved new drugs under section 505(a). Source sentence
Footnote 1 in each letter: 734884 "Despite statements on [the firm's] product labeling marketing [the firm's] products 'for research use only' ... evidence obtained from [the firm's] website establishes that [the firm's] products are intended to be drugs"; 735067 "'research use only', 'for research and laboratory use only'"; 735063 "'for research use only'"; 733652 "'for laboratory, research, and analytical use'"; 735127 "for 'research use only'"; 734884: "'Tesamorelin,' and 'BIMORELIN' are unapproved new drugs under section 505(a)"; section 505(a) in each letter: 735067, 735063, 733652 and 735127 each say "Based on our review, ... are unapproved new drugs under section 505(a) of the Federal Food, Drug, and Cosmetic Act" (733652 names 'Tesamorelin Ipamorelin Blend' among them; letter texts read 13 Oct 2026 from web.archive.org captures)1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 20262 FDA warning letter 735067 (TXP Innovations LLC dba Tex Peptides), 24 August 20263 FDA warning letter 735063 (Peptide Partners LLC), 24 August 20264 FDA warning letter 733652 (NuScience Peptides LLC), 24 August 20265 FDA warning letter 735127 (Peak Performance Peptides), 24 August 2026
What happened
US
- The letters went to Royal Peptides LLC (MARCS-CMS 734884), TXP Innovations LLC doing business as Tex Peptides (735067), Peptide Partners LLC (735063), NuScience Peptides LLC (733652) and Peak Performance Peptides (735127). The issuing office is FDA's Center for Drug Evaluation and Research. Source sentence
Letter headers: firm name, "MARCS-CMS" number and "August 24, 2026" on each letter; "Issuing Office: Center for Drug Evaluation and Research (CDER)" on each of 734884, 735067, 735063, 733652 and 735127 (735067, 735063, 733652 and 735127 read 13 Oct 2026 from web.archive.org captures)
1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 20262 FDA warning letter 735067 (TXP Innovations LLC dba Tex Peptides), 24 August 20263 FDA warning letter 735063 (Peptide Partners LLC), 24 August 20264 FDA warning letter 733652 (NuScience Peptides LLC), 24 August 20265 FDA warning letter 735127 (Peak Performance Peptides), 24 August 2026 - Each letter describes an FDA review of the firm's website and classifies named products as unapproved new drugs under section 505(a) of the FD&C Act. Across the five letters these include semaglutide, tirzepatide, retatrutide, SS-31 (elamipretide), PT-141 (bremelanotide), tesamorelin and a tesamorelin and ipamorelin blend. Source sentence
733652: "Based on our review, '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,' ... are unapproved new drugs under section 505(a)"; 734884: "Violations were identified and documented during a review of [the firm's] website royal-peptides.com in July 2026. Based on our review, 'Tirzepatide,' 'Semaglutide,' 'Retatrutide,' 'SS-31 (Elamipretide),' 'PT-141,' 'Tesamorelin,' and 'BIMORELIN' are unapproved new drugs under section 505(a)"; 735067: "Based on our review, 'Semaglutide (GLP-1 SEM),' 'Tirzepatide (GLP-2 TRZ),' 'Retatrutide (GLP-3 RT),' 'SS-31 (Elamipretide),' 'Tesamorelin,' 'PT-141 (Bremelanotide),' ... are unapproved new drugs under section 505(a)"; 735063: "Based on our review, 'GLP-1 S (Semaglutide),' 'GLP-2 T (Tirzepatide),' 'GLP-3 Reta (Retatrutide),' 'SS-31 (Elamipretide),' 'Tesa Peptide (Tesamorelin),' 'PT-141 (Bremelanotide),' ... are unapproved new drugs under section 505(a)"; 735127: "Based on our review, ... 'GLP-3R' (retatrutide), 'Semaglutide,' 'SS-31,' 'PT-141,' and 'Tesamorelin' are unapproved new drugs under section 505(a)"; each of the five letters: "This warning letter advises [the firm] of significant violations observed during a U.S. Food and Drug Administration (FDA) review of [the firm's] website." (letter texts read 13 Oct 2026 from web.archive.org captures, fda.gov answers 403 to this box)
1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 20262 FDA warning letter 735067 (TXP Innovations LLC dba Tex Peptides), 24 August 20263 FDA warning letter 735063 (Peptide Partners LLC), 24 August 20264 FDA warning letter 733652 (NuScience Peptides LLC), 24 August 20265 FDA warning letter 735127 (Peak Performance Peptides), 24 August 2026 - The Royal Peptides letter also names a product called BIMORELIN, which is not an Academy catalog compound. Source sentence
"'Tesamorelin,' and 'BIMORELIN' are unapproved new drugs under section 505(a)"
1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 2026 - The research statements quoted in the footnotes vary by seller, from "for research use only" and "for research and laboratory use only" to "for laboratory, research, and analytical use". Source sentence
Footnote 1 in each letter: 734884 "Despite statements on [the firm's] product labeling marketing [the firm's] products 'for research use only' ... evidence obtained from [the firm's] website establishes that [the firm's] products are intended to be drugs"; 735067 "'research use only', 'for research and laboratory use only'"; 735063 "'for research use only'"; 733652 "'for laboratory, research, and analytical use'"; 735127 "for 'research use only'"
1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 20262 FDA warning letter 735067 (TXP Innovations LLC dba Tex Peptides), 24 August 20264 FDA warning letter 733652 (NuScience Peptides LLC), 24 August 2026 - The Royal Peptides letter cites text from the firm's website as evidence of intended use as defined in 21 CFR 201.128. Source sentence
"Examples from [the firm's] product labeling, including on [the firm's] website, that provide evidence of the intended use (as defined in 21 CFR 201.128) of these products as drugs include"
1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 2026 - The footnotes also cite a water product sold alongside the peptides and, in two letters, a "peptide calculator"; one letter also names a "peptide guide". Source sentence
734884 footnote 1: "[the firm] market ... water alongside a 'peptide guide' and 'peptide calculator'"; 733652 footnote 1: "[the firm] market ... water alongside a 'peptide calculator'"; 735067 footnote 1: "[the firm] market ... water as a solvent"
1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 20264 FDA warning letter 733652 (NuScience Peptides LLC), 24 August 20262 FDA warning letter 735067 (TXP Innovations LLC dba Tex Peptides), 24 August 2026
Why it matters for researchers
- In the Royal Peptides letter, the evidence of intended use that FDA cites comes from the firm's product labeling including its website, not only from the label on a product. Source sentence
"Examples from [the firm's] product labeling, including on [the firm's] website, that provide evidence of the intended use"
1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 2026 - Among the cited passages are lines written in research language, such as a product "categorized under metabolic signaling research" and "Researchers studying incretin biology have long investigated the effects of GLP-1 and GIP receptor activity". Source sentence
Cited text: "Semaglutide Single Vials is categorized under metabolic signaling research."; "Researchers studying incretin biology have long investigated the effects of GLP-1 and GIP receptor activity."
1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 2026 - The Royal Peptides letter also quotes titles of published papers that the seller's PT-141 page listed, as part of the cited website text. Source sentence
734884, PT-141 section: product page text listing titles of published papers on PT-141, quoted in the letter
1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 2026 - One letter lists summaries of published studies, posted on the seller's product pages, among the evidence of intended use. Source sentence
735063: cited product page text quoting study summaries for tirzepatide ("This study ... tirzepatide ...")
3 FDA warning letter 735063 (Peptide Partners LLC), 24 August 2026
What is not known
- The letters describe reviews of websites; they do not report laboratory testing of any product. Source sentence
"Violations were identified and documented during a review of [the firm's] website"
1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 20262 FDA warning letter 735067 (TXP Innovations LLC dba Tex Peptides), 24 August 20263 FDA warning letter 735063 (Peptide Partners LLC), 24 August 20264 FDA warning letter 733652 (NuScience Peptides LLC), 24 August 20265 FDA warning letter 735127 (Peak Performance Peptides), 24 August 2026 - The Royal Peptides letter asks for a written response within fifteen business days; that response is not part of the published letter. Source sentence
Conclusion: "Send [the firm's] written response to FDAAdvisory@fda.hhs.gov within fifteen (15) business days of receipt"
1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 2026 - The Royal Peptides letter dates its website review to July 2026; changes to that website after the review are not covered by the letter. Source sentence
"Violations were identified and documented during a review of [the firm's] website royal-peptides.com in July 2026."
1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 2026
Compounds named in the letters
- Retatrutide
- Retatrutide: PubChem CID 171390338, formula C221H342N46O68, InChIKey MLOLQJNKXBNWFW-SAGGEDDASA-N. Source sentence
PubChem PUG REST: substance records named retatrutide (for example SID 438519203) map to CID 171390338; MolecularFormula C221H342N46O68; MolecularWeight 4731; InChIKey MLOLQJNKXBNWFW-SAGGEDDASA-N
6 PubChem CID 171390338 - Semaglutide
- Semaglutide: PubChem CID 56843331, formula C187H291N45O59, InChIKey DLSWIYLPEUIQAV-CCUURXOWSA-N. Source sentence
PubChem CID 56843331: title Semaglutide; synonyms include NN9535; MolecularFormula C187H291N45O59; MolecularWeight 4114; InChIKey DLSWIYLPEUIQAV-CCUURXOWSA-N
7 PubChem CID 56843331 - Tirzepatide
- Tirzepatide: PubChem CID 166567236, formula C225H348N48O68, InChIKey BTSOGEDATSQOAF-MCNPHUAVSA-N. Source sentence
PubChem CID 166567236: MolecularFormula C225H348N48O68; MolecularWeight 4813; InChIKey BTSOGEDATSQOAF-MCNPHUAVSA-N
8 PubChem CID 166567236 - SS-31 (elamipretide)
- SS-31 (elamipretide): PubChem CID 11764719, formula C32H49N9O5, InChIKey SFVLTCAESLKEHH-WKAQUBQDSA-N. Source sentence
PubChem CID 11764719: title Elamipretide; MolecularFormula C32H49N9O5; InChIKey SFVLTCAESLKEHH-WKAQUBQDSA-N
9 PubChem CID 11764719 - PT-141 (bremelanotide)
- PT-141 (bremelanotide): PubChem CID 9941379, formula C50H68N14O10, InChIKey FFHBJDQSGDNCIV-MFVUMRCOSA-N. Source sentence
PubChem CID 9941379: title Bremelanotide; MolecularFormula C50H68N14O10; InChIKey FFHBJDQSGDNCIV-MFVUMRCOSA-N
10 PubChem CID 9941379 - Tesamorelin
- Tesamorelin: PubChem CID 16137828, formula C221H366N72O67S, InChIKey QBEPNUQJQWDYKU-BMGKTWPMSA-N. Source sentence
PubChem CID 16137828: title Tesamorelin; MolecularFormula C221H366N72O67S; InChIKey QBEPNUQJQWDYKU-BMGKTWPMSA-N
11 PubChem CID 16137828
Regulator actions
US
- , US, FDA (CDER), warning letter: MARCS-CMS 734884 to Royal Peptides LLC, after a July 2026 review of its website; named products, including tirzepatide, semaglutide, retatrutide, SS-31, PT-141, tesamorelin and BIMORELIN, classed as unapproved new drugs under section 505(a). 1 FDA warning letter 734884 (Royal Peptides LLC), 24 August 2026
- , US, FDA (CDER), warning letter: MARCS-CMS 735067 to TXP Innovations LLC doing business as Tex Peptides, after a website review; named products, including semaglutide, tirzepatide, retatrutide, SS-31, tesamorelin and PT-141, classed as unapproved new drugs under section 505(a). 2 FDA warning letter 735067 (TXP Innovations LLC dba Tex Peptides), 24 August 2026
- , US, FDA (CDER), warning letter: MARCS-CMS 735063 to Peptide Partners LLC, after a website review; named products, including semaglutide, tirzepatide, retatrutide, SS-31, tesamorelin and PT-141, classed as unapproved new drugs under section 505(a); the letter cites study summaries from the product pages. 3 FDA warning letter 735063 (Peptide Partners LLC), 24 August 2026
- , US, FDA (CDER), warning letter: MARCS-CMS 733652 to NuScience Peptides LLC, after a website review; named products, including tirzepatide, semaglutide, retatrutide, survodutide, mazdutide, PT-141, tesamorelin and a tesamorelin and ipamorelin blend, classed as unapproved new drugs under section 505(a). 4 FDA warning letter 733652 (NuScience Peptides LLC), 24 August 2026
- , US, FDA (CDER), warning letter: MARCS-CMS 735127 to Peak Performance Peptides, after a website review; named products, including retatrutide, semaglutide, SS-31, PT-141 and tesamorelin, classed as unapproved new drugs under section 505(a). 5 FDA warning letter 735127 (Peak Performance Peptides), 24 August 2026
Sources
- 1FDA warning letter 734884 (Royal Peptides LLC), 24 August 2026 accessed 13 Oct 2026
- 2FDA warning letter 735067 (TXP Innovations LLC dba Tex Peptides), 24 August 2026 accessed 13 Oct 2026
- 3FDA warning letter 735063 (Peptide Partners LLC), 24 August 2026 accessed 13 Oct 2026
- 4FDA warning letter 733652 (NuScience Peptides LLC), 24 August 2026 accessed 13 Oct 2026
- 5FDA warning letter 735127 (Peak Performance Peptides), 24 August 2026 accessed 13 Oct 2026
- 6PubChem CID 171390338 accessed 13 Oct 2026
- 7PubChem CID 56843331 accessed 13 Oct 2026
- 8PubChem CID 166567236 accessed 13 Oct 2026
- 9PubChem CID 11764719 accessed 13 Oct 2026
- 10PubChem CID 9941379 accessed 13 Oct 2026
- 11PubChem CID 16137828 accessed 13 Oct 2026
About this page
Research-use information. This library summarises published literature and regulator records. It is not guidance for use, not medical advice, and not a statement that any material is suitable for use in people or animals.
Reviewed by the Peptency editorial process. Version 2, last edited 13 October 2026, 11 sources.
Cite this page: Peptency Academy. FDA warning letters, 24 Aug 2026: retatrutide, semaglutide sellers. Version 2./us/academy/news/fda-warning-letters-research-use-only-august-2026/