Yes. GLP-3 RT is retatrutide, Eli Lilly's investigational GLP-1/GIP/glucagon triple agonist (LY3437943). FDA's warning letters of 24 August 2026 identify "GLP-3 RT (Retatrutide)", "GLP-3R" and "GLP-3 Reta (Retatrutide)" as retatrutide and treat them as unapproved new drugs, the same as vials labelled with the real name. Lilly calls "GLP-3" "a scientifically inaccurate label". There is no GLP-3 receptor, and no approved retatrutide product exists under any name.
Is GLP-3 RT the same as retatrutide?
Yes. "GLP-3 RT" is retatrutide under a vendor label. FDA's warning letter to Tex Peptides, dated 24 August 2026, names the product "GLP-3 RT (Retatrutide)". Vendors selling it print retatrutide's registry number, CAS 2381089-83-2, on the same page. The label changes; the molecule does not.
There is no GLP-3 receptor. Retatrutide activates three receptors: GLP-1, GIP and glucagon. Lilly's own explainer puts it bluntly: "The term 'GLP-3' is a scientifically inaccurate label used informally in the media to describe triple hormone receptor agonists" (Lilly, updated September 2026).
Did FDA accept the code name?
No. FDA's Center for Drug Evaluation and Research sent five warning letters dated 24 August 2026 and posted 1 September. Four of them name retatrutide under a code name, and FDA supplies the real name each time:
- Peak Performance Peptides (735127): "'GLP-3R' (retatrutide)"
- Tex Peptides / TXP Innovations (735067): "GLP-3 RT (Retatrutide)"
- NuScience Peptides (733652): "GLP-3 RT (Retatrutide) Research Peptide"
- Peptide Partners (735063): "GLP-3 Reta (Retatrutide)"
The fifth letter, to Royal Peptides (734884), covers a vial sold as plain "Retatrutide". All five reach the same conclusion: the products are unapproved new drugs. The four code-name letters each quote the vendor's "research use only" wording and reject it. The Peak Performance letter reads: "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."
Two kinds of evidence recur. All five letters cite bacteriostatic water sold next to the peptides, and four of them list it as an unapproved drug in its own right; the Royal Peptides letter raises it only in a footnote. The NuScience and Royal letters also cite a "peptide calculator" as evidence of intended human use.
The pattern predates August. On 31 March 2026 FDA wrote to Gram Peptides (721806) about "Retatrutide" that the firm "also referred to … as 'GLP-1-R peptide'", and to PekCura Labs (721709) about "GLP-3-R" in "all variations". A code name moves a listing out of some keyword filters. It has not moved anything out of an FDA letter.
The wider August round, including Lilly's six lawsuits against online sellers, is covered in FDA's August 2026 peptide letters and Lilly's lawsuits.
Which vendors sell retatrutide as GLP-3 RT?
The table joins two sources: the FDA letters, and our mirrors of public COA records (Janoshik, crawled 30 June 2026; Kovera, synced 1 August 2026). "Purity" is the HPLC figure on the record. "Content" is the measured milligrams against the label.
| Label as sold | Seller | FDA warning letter | Public COA in our mirrors |
|---|---|---|---|
| "GLP-3R" | Peak Performance Peptides | 735127, 24 Aug 2026 | none found |
| "GLP-3 RT (Retatrutide)" | Tex Peptides | 735067, 24 Aug 2026 | none found |
| "GLP-3 RT (Retatrutide) Research Peptide" | NuScience Peptides | 733652, 24 Aug 2026 | none found |
| "GLP-3 Reta (Retatrutide)" | Peptide Partners | 735063, 24 Aug 2026 | 3 Kovera COAs filed as "Retatrutide", June–July 2026: 99.36–99.78% (audit) |
| "GLP-3-R" | PekCura Labs | 721709, 31 Mar 2026 | none found |
| "GLP-1-R peptide" | Gram Peptides | 721806, 31 Mar 2026 | none found |
| "GLP-3 R 30mg" | Penguin Peptides | none found | Janoshik 100668: 99.88%, 32.33 mg of 30 mg |
| "GLP-3RT 20mg" | MaximumPeps | none found | Janoshik 101176: 99.71%, 20.94 mg of 20 mg |
| "GLP3-R" | not named on the record | n/a | Kovera KVR-2026-5D8D49: 99.94% |
| "GLP-3 RT" | Research Peptide Hub | none found | Freedom Diagnostics COAs on the vendor's site |
| "Triple Receptor Agonist" (formerly "GLP-3") | Panda Peptides | none found | vendor-published Janoshik 231312 and 231316 (Sep 2026): 99.52–99.83%, analyte named as retatrutide |
| "GLP3-RT (Trinity-X)" | Real Peptides | none found | Freedom Diagnostics and Kovera COAs on the vendor's site; none in our mirrors |
| "Retatrutide" (real name), all sellers | Janoshik median 99.78% (65 tests); Kovera median 99.89% (231 COAs) |
"None found" in the FDA column means our search of FDA's warning-letter pages on 5 October 2026 returned nothing for that seller.
What the table shows: the three code-named vials with public COAs tested clean and close to label. In this small sample, a code name did not predict a bad vial. Across all 323 retatrutide results we mirror, two of the three identity failures were code-named; our retatrutide lab-record analysis has the counts. Purity is also the wrong single number to read: across 58 Janoshik retatrutide tests that report both, measured content ran from 87.8% to 143.5% of label. A 99.9% pure vial holding 40% extra peptide still misleads anyone reading the label. Kovera COAs carry a separate caveat, covered in our Kovera COA revisions audit.
How we know it's retatrutide without the FDA letters
Three identifiers appear on vendor listings that use the GLP-3 name:
- CAS 2381089-83-2. Retatrutide's registry number. A CAS number belongs to a compound and does not change with a brand name.
- The structure. Retatrutide is a 39-amino-acid peptide conjugated to a C20 fatty diacid, per Lilly's Phase 1b paper (The Lancet 2022). An earlier version of this page said C18; that was wrong.
- The triple-receptor description. GLP-1, GIP and glucagon. No other peptide in the research market claims that profile.
NuScience's own listing, as FDA quotes it, says the product is "also known as LY3437943", Lilly's development code for retatrutide.
GLP-3 RT vs "GLP-2 TRZ" and the other house names
The same naming scheme runs across the GLP-1 drugs. In the 24 August letters FDA quotes "GLP-1 S (Semaglutide)", "GLP-2 T (Tirzepatide)", "GLP-2 Tirz Peptide" and "GLP-1 Sema Research Peptide". The number counts receptors, not generations:
- GLP-1 S / GLP-1 Sema → semaglutide, one receptor.
- GLP-2 T / GLP-2 TRZ → tirzepatide, two receptors (GLP-1, GIP).
- GLP-3 R / GLP-3 RT / GLP-3 Reta → retatrutide, three receptors.
"GLP-2" in this scheme is not the real hormone GLP-2, which is a separate peptide with a separate receptor. That collision is one more reason the labels mislead. The compound comparison is at retatrutide vs tirzepatide, and the broader pattern at code-name catalogs and FDA evasion.
Reading the dose-size notation
Numbers appended to the label, as in "GLP-3 RT 20" or "RT-30", are vial sizes in milligrams, not doses. The trial dose steps are documented at retatrutide dosing protocols and the reported side effects at retatrutide side effects. We state vial size; we do not recommend a human dose.
How to verify a GLP-3 RT listing
Treat any "GLP-3 RT" listing as unverified until it clears the checks we apply to a listing that uses the real name:
- CAS on the listing reads 2381089-83-2.
- A per-batch COA resolves in the lab's own public index. Paste it into /tools/coa-verifier.
- Mass-spec identity is on the COA, not only an HPLC purity figure.
- The seller is not named in an FDA warning letter. Search the FDA warning-letter database.
The legal and market picture for buyers, including Lilly's expanded-access program, is at where to buy retatrutide.
Sources
- FDA warning letter, Peak Performance Peptides, 735127, 24 August 2026
- FDA warning letter, TXP Innovations LLC dba Tex Peptides, 735067, 24 August 2026
- FDA warning letter, NuScience Peptides LLC, 733652, 24 August 2026
- FDA warning letter, Peptide Partners LLC, 735063, 24 August 2026
- FDA warning letter, Royal Peptides LLC, 734884, 24 August 2026
- FDA warning letter, Gram Peptides, 721806, 31 March 2026
- FDA warning letter, PekCura Labs, 721709, 31 March 2026
- Eli Lilly, "What to know about retatrutide", updated September 2026
- Urva et al., retatrutide Phase 1b, The Lancet 2022
- Internal: where to buy retatrutide, FDA's August 2026 letters and Lilly's lawsuits, code-name catalogs and FDA evasion, how to spot aliased peptide vendors, Kovera COA revisions
Frequently asked
Is GLP-3 RT the same as retatrutide?
Yes. FDA's 24 August 2026 warning letters to Tex Peptides and NuScience Peptides name the product "GLP-3 RT (Retatrutide)". Vendors selling it list retatrutide's CAS number, 2381089-83-2, on their own pages. "RT" abbreviates retatrutide; "GLP-3" is a label for its three-receptor action. The molecule is the same.
What does GLP-3 RT stand for?
"GLP-3" is not a receptor or a drug class. There is no GLP-3 receptor. Vendors use it to suggest a third-generation incretin that hits three receptors (GLP-1, GIP and glucagon). Lilly calls "GLP-3" "a scientifically inaccurate label". "RT" stands for retatrutide.
Did FDA accept GLP-3 RT as a different product from retatrutide?
No. In five letters dated 24 August 2026, FDA identified code-named products as retatrutide, semaglutide and tirzepatide and called them unapproved new drugs. Royal Peptides sold its vial as plain "Retatrutide" and received the same kind of letter. The code name changed nothing in FDA's analysis.
Which vendors sell retatrutide as GLP-3?
FDA's letters name Peak Performance Peptides ("GLP-3R"), Tex Peptides and NuScience Peptides ("GLP-3 RT"), Peptide Partners ("GLP-3 Reta") and, in March 2026, PekCura Labs ("GLP-3-R"). Our COA mirrors add Penguin Peptides ("GLP-3 R") and MaximumPeps ("GLP-3RT"). The table on this page lists each with its COA record.
What does GLP-3 RT 20 or RT-30 mean?
The trailing number is the vial size in milligrams. "GLP-3 RT 20" is a 20 mg vial and "RT-30" is 30 mg. It is not a dose. The doses used in the TRIUMPH trials are on our retatrutide dosing protocols page. We do not recommend any human dose.
How do I verify that GLP-3 RT is actually retatrutide?
Check three things. The listing should give CAS 2381089-83-2. The COA should resolve on the testing lab's own site, not just as a vendor PDF. And the COA should report mass-spec identity, not only HPLC purity. Purity says how clean a sample is; identity says which molecule it is.
Is GLP-3 RT legal to buy?
Retatrutide is not a controlled substance, but it is not approved for any use. FDA's August 2026 letters treat code-named retatrutide sold with bacteriostatic water as an unapproved new drug intended for human use, despite "research use only" labels. Renaming it does not change its status. See our peptide legality tool for per-compound detail.