Retatrutide
Triple GIP / GLP-1 / glucagon receptor agonist · Research-grade reference material
Identity
- Molecular formula
- C221H342N46O68 (reported as C228H350N48O66 in at least one other database — confirm against reference standard before publishing)
- Molecular weight
- ~4731.4 g/mol (a second source reports ~4894.6 g/mol — same flag as above)
- CAS number
- 2381089-83-2
Research Background
Retatrutide (LY3437943) is Eli Lilly’s investigational triple agonist, engineered to activate three separate metabolic receptors: GLP-1, GIP, and glucagon. It binds human GCGR, GLP-1R, and GIPR with EC50 values of 5.79 nM, 0.775 nM, and 0.0643 nM respectively.
The engineering approach behind retatrutide traces back further than the molecule itself: researchers first combined glucagon and GLP-1 activity in a single molecule in rodents in 2009 (Day et al.), and a rationally designed triple agonist correcting both obesity and diabetes in animal models followed in 2015 (Finan et al.). Coskun and colleagues carried that concept into the first human proof of concept in 2022 (Coskun et al.), and the Phase 2 trial that drew wider attention published in 2023 (Jastreboff et al.).
Lab-tested research material
Mechanism
Unlike single-target GLP-1 drugs or dual GLP-1/GIP agonists, retatrutide adds glucagon receptor activity, historically avoided in this drug class because glucagon raises blood glucose. The GLP-1 and GIP components are studied for offsetting that effect while capturing glucagon’s upside: increased energy expenditure and more direct fat breakdown in the liver and visceral tissue.
Retatrutide extends incretin co-agonism to a third target. Where dual agonists engage the appetite and insulin axes, adding glucagon receptor agonism introduces a direct energy-expenditure and lipolytic signal, a mechanistically different contribution rather than simply more of the same.
GIP receptor agonism. Incretin signaling; insulin response and adipose-tissue effects.
GLP-1 receptor agonism. Appetite reduction and slowed gastric emptying, as in the established GLP-1 class.
Glucagon receptor agonism. Associated with increased energy expenditure and fat metabolism, the differentiating component.
Once-weekly pharmacokinetics. Fatty-acid modification supports extended half-life in the investigational clinical formulation.
Open scientific question. Whether the added glucagon signal alters the long-term safety profile relative to dual agonism is precisely what the ongoing Phase 3 programme is designed to determine.
Triple hormone receptor co-agonism. Schematic. Research-grade material supplied here is for in-vitro laboratory use only.
State of the Evidence
Research Evidence: based on 2 sources cited, most recent 2023. Regulatory Status: Investigational. Not approved by the FDA, EMA, or any regulatory body for any indication. Lilly has indicated a regulatory submission for weight management could come in late 2026; submission is not approval, and no timeline is guaranteed. Availability Status: Research Only.
Phase 3 data (the TRIUMPH program) is actively reporting across multiple indications as of this writing. Findings to date are substantial but remain investigational; retatrutide has not completed the regulatory approval process anywhere in the world.
1. Human · Phase 2 RCT — “Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial,” New England Journal of Medicine, 2023. DOI 10.1056/NEJMoa2301972
2. Discovery / Mechanistic — “LY3437943, a Novel Triple Glucagon, GIP, and GLP-1 Receptor Agonist for Glycemic Control and Weight Loss,” Cell Metabolism, 2022. Vol. 34, no. 9, pp. 1234-1247
What the Literature Supports — and What It Doesn’t
Retatrutide has produced striking Phase 3 topline results. It is nonetheless investigational: no regulatory authority has approved it, most Phase 3 readouts are pending, and much of the currently public data is company topline rather than full peer-reviewed publication.
Evidence at a glance
TRIUMPH-1 (NCT05929066; N=2,339, 80 weeks, obesity/overweight without diabetes): all doses (4 / 9 / 12 mg) met primary and key secondary endpoints, with placebo-adjusted mean weight reduction reported across doses versus 2.2% placebo. Topline announced May 2026.
TRIUMPH-4 (obesity with knee osteoarthritis, 68 weeks): met co-primary endpoints for weight and pain/physical function. Topline announced December 2025.
Phase 2 data published 2023 supported progression to Phase 3.
Seven additional Phase 3 readouts were expected during 2026, spanning type 2 diabetes, OSA, chronic low back pain, cardiovascular/renal outcomes and MASLD. The full picture is not yet complete.
Much public data remains topline / conference-presented rather than fully peer-reviewed, and independent scrutiny of complete datasets is limited.
Appropriate characterization: a first-in-class triple agonist with strong but still-accumulating late-stage clinical evidence, no regulatory approval in any jurisdiction, and an incompletely characterized long-term safety profile. Information here is current as of the revision date; the TRIUMPH programme is actively reading out and this section should be re-verified before reuse.
Regulatory & status notes
Selected references
- 1. Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity — a Phase 2 trial. N Engl J Med. 2023.
- 2. Eli Lilly and Company. TRIUMPH-1 Phase 3 topline results (NCT05929066). May 2026.
- 3. Eli Lilly and Company. TRIUMPH-4 Phase 3 topline results, obesity with knee osteoarthritis. December 2025.
- 4. TRANSCEND-T2D-1 and TRIUMPH-1 results, ADA Scientific Sessions 2026.
Safety Information
Research-use compound with limited human data. Evidence strength varies — see the Evidence section above.
No established clinical contraindications. This is an investigational compound with limited human data and has not been evaluated by the FDA for safety in this context. Consult a qualified clinician. For research and educational purposes only, not for human or veterinary use.
Related Compounds
For research and educational purposes only. Not for human or veterinary use.