Retatrutide
Retatrutide peptide · LY3437943 · reta · retatrutid · retratrutide · retatrutida
Coming soon
What Retatrutide is
Retatrutide (development code LY3437943) is a synthetic 39-amino-acid peptide designed by Eli Lilly to activate three hormone receptors at once: GIP, GLP-1 and glucagon. It is built on an incretin-style backbone with several unnatural residues and a fatty-acid side chain attached to one lysine, a design used to make peptides last longer in the body. Lilly scientists described its discovery and first human study in Cell Metabolism in 2022.
Retatrutide is investigational. It has been studied in randomized Phase 2 and Phase 3 trials sponsored by Lilly, several of which have been published, but it is not approved by the FDA and is not a prescription medicine. That means any vial sold outside a clinical trial is research-grade or unapproved product with no regulatory check on what is inside. Because the molecule is large and carries several modifications that are easy to get wrong in synthesis, independent lot testing for identity, purity, peptide content and contamination is the only way to know what a given vial actually contains.
| Sequence | Tyr-Aib-Gln-Gly-Thr-Phe-Thr-Ser-Asp-Tyr-Ser-Ile-αMeLeu-Leu-Asp-Lys-Lys(AEEA-γGlu-C20 diacid)-Ala-Gln-Aib-Ala-Phe-Ile-Glu-Tyr-Leu-Leu-Glu-Gly-Gly-Pro-Ser-Ser-Gly-Ala-Pro-Pro-Pro-Ser-NH2 |
|---|---|
| One-letter code | Y[Aib]QGTFTSDYSI[αMeL]LDK[K*]AQ[Aib]AFIEYLLEGGPSSGAPPPS-NH2 |
| Length | 39 amino acids |
| Molecular formula | C221H342N46O68 |
| Molecular weight | ≈4731.3 Da |
| Expected m/z | [set when the lab validates the method] |
Modifications and look-alikes
Modifications
Four non-standard features. (1) Position 2 and position 20 are Aib (2-aminoisobutyric acid, alpha-methylalanine), not Ala. (2) Position 13 is alpha-methyl-leucine, not Leu. (3) Lys17 carries a lipid side chain on its epsilon-amine: a C20 fatty diacid (eicosanedioic acid) joined through a gamma-Glu spacer and an AEEA linker (8-amino-3,6-dioxaoctanoic acid), written Lys(AEEA-γGlu-C20 diacid). (4) The C-terminal Ser39 is amidated (-NH2). Reference monoisotopic mass for the free (non-salt) form is 4728.47 Da (KEGG D12430); the average 4731.3 Da figure is the free form.
What it gets confused with
(a) Salt form: FDA GSRS lists a separate substance, retatrutide sodium (UNII LQ42M82ZU6), alongside retatrutide (UNII NOP2Y096GV); research vials may also carry TFA or acetate counterions, so gross vial weight is not peptide content. (b) One-letter notation differs between databases: GSRS writes the Aib positions as A and alpha-methyl-Leu as L, KEGG writes Aib as X; neither plain string shows the Lys17 lipid, so a "sequence match" on a plain string alone does not confirm identity. (c) Products sold as "reta" may contain a different GLP-1 class peptide (e.g. semaglutide, tirzepatide) or a mislabelled mix; these differ in mass and are distinguished by LC-MS. (d) Do not confuse with tirzepatide (dual GIP/GLP-1) or survodutide/mazdutide (dual GLP-1/glucagon).
Identity sources: rest.kegg.jp · gsrs.ncats.nih.gov · file.medchemexpress.com · doi.org
Regulatory status. Not FDA-approved. Retatrutide is an investigational drug available only through clinical trials (drugs.com FDA approval status, checked 2026-10-12: https://www.drugs.com/history/retatrutide). Eli Lilly has reported Phase 3 results and has a planned FDA submission in early 2027 (Epocrates, 2026-07-24: https://www.epocrates.com/online/article/retatrutide-heads-toward-fda-filing-after-positive-phase-3-obesity-trial-results). Any retatrutide sold to the public today is unapproved or research-use-only material.
Read the research summary and referencesRetatrutide test results
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