A 39-amino-acid triple agonist of the GLP-1, GIP, and glucagon receptors (CAS 2381089-83-2), developed by Eli Lilly as LY3437943. Adds glucagon-receptor activity on top of the GLP-1/GIP mechanism of tirzepatide. Lilly has reported positive Phase 3 results in adults with obesity and plans to file for U.S. approval, and it is not FDA-approved. Sold by research vendors under codes including GLP3-R, RETA-3, R-30.
Retatrutide (Eli Lilly's LY3437943) is a 39-amino-acid synthetic peptide that activates three incretin and glucagon-related receptors simultaneously: the GLP-1 receptor (the same target as semaglutide), the GIP receptor (the second target tirzepatide adds), and the glucagon receptor (the new addition in retatrutide). Lilly describes it as a triple hormone receptor agonist.
The third receptor is what differentiates retatrutide from tirzepatide. In Lilly's studies in obese mice, glucagon-receptor activity added an increase in energy expenditure to the reduced calorie intake driven by the GLP-1 and GIP receptors (Coskun and colleagues, Cell Metabolism, 2022).
Phase 3 trial results
Lilly's Phase 3 program for retatrutide is called TRIUMPH. The figures below come from Lilly's announcements and use the efficacy estimand, which estimates the effect had every participant stayed on treatment. Analyses that count outcomes regardless of discontinuation report smaller reductions: 25.0% versus 28.3% in TRIUMPH-1, for example.
TRIUMPH-4 (obesity with knee osteoarthritis, December 2025): 28.7% mean body-weight reduction at 68 weeks in the highest-dose group, versus 2.1% with placebo.
TRIUMPH-1 (obesity or overweight without diabetes, May 2026): 28.3% at 80 weeks in the highest-dose group, versus 2.2% with placebo, across 2,339 participants.
TRIUMPH-2 (type 2 diabetes with obesity or overweight, September 2026): 20.8% at 80 weeks versus 4.0% with placebo, with mean A1C reductions of 1.4 to 1.6 percentage points versus 0.2.
TRIUMPH-3 (severe obesity with established cardiovascular disease, July 2026): up to 22.6% at 80 weeks in topline results, versus 3.2% with placebo, with detailed results not yet published.
TRIUMPH-2 enrolled 1,152 adults and was published in The Lancet. Lilly reported that 59.5% of its highest-dose group no longer met the BMI criteria for obesity at 80 weeks. The trials enrolled different populations over different periods, so their figures are not directly comparable with one another. Earlier Phase 2 results, published in The New England Journal of Medicine in 2023, had pointed to a similar magnitude of effect.
The obstructive sleep apnea substudies of TRIUMPH-1 and TRIUMPH-2, 691 adults in all, were published in The New England Journal of Medicine in October 2026. At 80 weeks the two higher doses lowered the apnea-hypopnea index (breathing pauses and shallow-breathing episodes per hour of sleep) by 22.5 to 24.7 events per hour more than placebo in adults without diabetes and by 13.9 to 15.0 in adults with type 2 diabetes, from baseline averages near 59 and 56, counting all randomized participants. Further trials are under way in chronic low back pain, cardiovascular and renal outcomes, and metabolic dysfunction-associated steatotic liver disease. TRIUMPH-5 compares retatrutide directly with tirzepatide in adults with obesity and, as of October 2026, has not reported results. Until it does, no trial has compared the two compounds head to head. Retatrutide vs tirzepatide vs semaglutide covers why separate trials cannot rank them.
FDA approval timeline
Retatrutide is not approved by the FDA for any indication. Lilly said in July and September 2026 that it plans to submit a Biologics License Application (BLA) in the first quarter of 2027, once its chemistry, manufacturing and controls package is complete, and that its clinical data support submissions for obesity, knee osteoarthritis pain and obstructive sleep apnea.
A BLA is the application for a biological product rather than a drug. FDA classified retatrutide as a drug in March 2024 and reached the same conclusion on October 2, 2026, after a district court sent the question back to it, and Lilly's challenge is still in the courts. Our writeups of the September 2026 appeal and FDA's October 2026 decision explain what the classification changes.
Lilly states that retatrutide is legally available only to participants in its clinical trials, and in June 2026 it registered a single-patient expanded access program for adults with severe obesity and serious complications who cannot join one. As an investigational compound it has no USP monograph and is not a component of any approved drug, and FDA states that it cannot be used in compounding under federal law. FDA has also warned companies that sold unapproved retatrutide falsely labeled "for research purposes" or "not for human consumption." Eli Lilly has also sued businesses it says sell retatrutide, and our post on Lilly's retatrutide lawsuits tracks where each case stands.
Vendor naming conventions
Retatrutide is sold under an unusually large number of vendor-specific product codes. Common examples include GLP3-R, GLP-3, R-30, RETA-3, EZP-3P, FG3-R, and a long list of variants. The full set of codes used by the vendors that PeptideScouter tracks is visible in the "Also known as" strip at the top of this page.
The dominant pattern is "GLP-N" generational naming: GLP1 typically refers to semaglutide, GLP2 to tirzepatide, and GLP3 to retatrutide. This convention is informal and reflects drug generation rather than the underlying scientific nomenclature (semaglutide is a GLP-1 receptor agonist, tirzepatide a GLP-1/GIP dual agonist and retatrutide a GLP-1/GIP/glucagon triple agonist). Numeric suffixes within codes such as R-30 and R-10 typically encode the vial size in milligrams and carry no structural meaning. Our post on what GLP-3 means explains where the nickname came from and why no hormone carries the name.
Vendors generally avoid using the literal word "retatrutide" in product titles. PeptideScouter normalizes all known vendor codes back to the canonical peptide identity so that prices across vendors can be compared on a per-milligram basis regardless of how each vendor labels the product.
Frequently asked questions
When is retatrutide expected to be FDA approved?
Eli Lilly has said it plans to file for FDA approval of retatrutide in the first quarter of 2027, after completing its chemistry, manufacturing and controls package, and that its clinical data support submissions for obesity, knee osteoarthritis pain and obstructive sleep apnea. An approval date cannot be known until the FDA has the application. As of October 2026, retatrutide is not approved for any indication and is not available from any U.S. pharmacy.
How does retatrutide differ from tirzepatide and semaglutide?
Semaglutide activates a single receptor (GLP-1). Tirzepatide activates two (GLP-1 and GIP). Retatrutide activates three: GLP-1, GIP, and the glucagon receptor. In Lilly's studies in obese mice, the glucagon-receptor activity added an increase in energy expenditure to the reduced food intake driven by the other two receptors. TRIUMPH-5, a Phase 3 trial comparing retatrutide directly with tirzepatide, had not reported results as of October 2026, so no trial has yet compared retatrutide and tirzepatide head to head.
Why does retatrutide have so many different vendor codes?
Each vendor coins its own code, and vendors generally avoid the name "retatrutide" in product titles. The codes follow an informal generational pattern: GLP1 commonly refers to semaglutide, GLP2 to tirzepatide, and GLP3 to retatrutide, with codes like GLP3-R, R-30, RETA-3, and EZP-3P building on that convention. Numeric suffixes typically encode vial size in milligrams. PeptideScouter normalizes every known code back to the canonical peptide so prices remain comparable across vendors.
Can I buy FDA-approved retatrutide?
No. Retatrutide is in Phase 3 clinical trials and has not been submitted for FDA approval. Eli Lilly plans to file for FDA approval in the first quarter of 2027. It is not available from licensed U.S. pharmacies, including compounding pharmacies, and Lilly states it is legally available only to participants in its clinical trials, apart from a single-patient expanded access program it registered in June 2026. Research-grade material sold by peptide vendors is for research purposes only and not for human consumption.
Where can I buy Retatrutide online?
Retatrutide is sold by 46 research peptide vendors indexed on PeptideScouter, with 284 tracked listings compared per vendor in the table above. Pricing is normalized and refreshed daily.
Is Retatrutide in stock right now?
All 46 indexed research peptide vendors currently have Retatrutide in stock. Stock state is refreshed daily from each vendor's catalog.
What is the cheapest place to buy Retatrutide?
Studz Peptides currently lists Retatrutide at $1.00/mg, the lowest listed price across 46 tracked research peptide vendors. With current vendor discount codes applied, the lowest effective price is $0.90/mg.
Is there a discount code for Retatrutide?
Discount codes are issued per vendor rather than per peptide, so any code applies across that vendor's whole catalog. 45 of the 46 vendors listing Retatrutide publish a PeptideScouter code, worth 5% to 50% off. Applied, the lowest effective price falls from $1.00/mg listed to $0.90/mg at Studz Peptides. Each vendor's code is shown beside its price in the table above.
How much does Retatrutide cost per mg?
Retatrutide ranges from $1.00/mg to $17.00/mg across 284 listings from 46 research peptide vendors, normalized to USD per milligram and refreshed daily.
How many vendors sell Retatrutide?
46 research peptide vendors currently list Retatrutide on PeptideScouter. We track 284 listings across size and kit variants.
What is the CAS number for Retatrutide?
Retatrutide's CAS Registry Number is 2381089-83-2. It is also sold as GLP3-R, GLP3-Reta, R-30.
