Retatrutide
Retatrutide (LY3437943): A Triple GLP-1 / GIP / Glucagon Receptor Agonist
Research summary. Retatrutide is a once-weekly synthetic peptide developed by Eli Lilly that acts as a triple agonist at the GLP-1, GIP, and glucagon receptors. It represents the next evolutionary step beyond GLP-1 monoagonists (semaglutide, liraglutide) and the GLP-1/GIP dual agonist tirzepatide, adding glucagon-receptor agonism to drive additional energy expenditure and hepatic-fat reduction. Phase 2 results published in NEJM in 2023 reported weight reductions exceeding 24% at 48 weeks at the highest doses — among the largest pharmacological weight reductions ever reported in a registration-track trial.
Molecular profile
- Class: GLP-1 / GIP / glucagon triple receptor agonist (peptide)
- Molecular formula: C₁₇₉H₂₈₈N₅₀O₅₂
- Molecular weight: ~3998.6 g/mol
- Synonyms: LY3437943
- Half-life: Approximately six days, supporting once-weekly subcutaneous administration
- Modification: Fatty-acid conjugation (similar to semaglutide and tirzepatide design strategy) to support albumin-mediated half-life extension
Mechanism of action
Retatrutide layers three incretin/glucoregulatory mechanisms onto a single peptide:
- GLP-1 receptor agonism. Glucose-dependent insulin secretion, glucagon suppression, delayed gastric emptying, and central appetite suppression — the established GLP-1 mechanism shared with semaglutide and dulaglutide.
- GIP receptor agonism. Additional glucose-dependent insulin release and effects on adipose-tissue insulin sensitivity, shared with tirzepatide.
- Glucagon receptor agonism. The differentiating mechanism. Glucagon-receptor agonism increases hepatic energy expenditure, supports fatty-acid oxidation, and may directly reduce hepatic triglyceride content. The trick of the molecule is balancing this with sufficient GLP-1 incretin activity to avoid net hyperglycaemia.
This mechanistic stacking is intended to combine the glycaemic and weight-loss effects of GLP-1/GIP agonists with additional fat-mass and hepatic-steatosis effects mediated by glucagon-receptor activation.
Clinical research highlights
Phase 2 obesity trial (Jastreboff et al., NEJM 2023). A 48-week randomised, double-blind, placebo-controlled Phase 2 trial in adults with obesity reported dose-dependent weight reductions reaching approximately 24.2% from baseline at the 12 mg dose, with treatment effects clearly separating from placebo. The safety profile resembled that of other incretin agonists, with gastrointestinal adverse effects (nausea, diarrhoea, vomiting) the most commonly reported.
Phase 2 type-2-diabetes trial (Rosenstock et al., Lancet 2023). A 36-week trial in adults with type 2 diabetes reported substantial reductions in HbA1c and body weight relative to placebo, with weight reductions notably larger than those typically reported with GLP-1 monoagonists or with GLP-1/GIP dual agonism.
Hepatic-steatosis endpoints. Sub-analyses in patients with elevated hepatic fat have reported substantial reductions in liver fat content, consistent with the glucagon-receptor mechanism's reported effect on hepatic lipid handling.
Phase 3 programme (TRIUMPH). The TRIUMPH Phase 3 development programme evaluating retatrutide in obesity, type 2 diabetes, obstructive sleep apnoea, knee osteoarthritis, and other indications is ongoing.
Current research status
Retatrutide is an investigational drug in late-stage clinical development. As of mid-2026 it has not been approved by the FDA. Eli Lilly's Phase 3 TRIUMPH programme is the registration-track effort that will support a New Drug Application.
Research-peptide supply of triple-agonist material is broadly available, but the regulated drug product — once approved — will be the appropriate channel for clinical use. Research-grade material is for laboratory and animal-model use only.
Key takeaways for researchers
- Retatrutide is a once-weekly triple GLP-1 / GIP / glucagon receptor agonist developed by Eli Lilly.
- The glucagon-receptor mechanism differentiates it from GLP-1 monoagonists (semaglutide) and GLP-1/GIP dual agonists (tirzepatide), targeting additional energy expenditure and hepatic-fat handling.
- Phase 2 trials reported approximately 24% weight reduction at 48 weeks at the highest doses, the largest reductions reported in a registration-track obesity trial to date.
- Phase 3 TRIUMPH programme is ongoing across obesity, T2D, OSA, and other indications.
- Retatrutide is not currently FDA-approved; research-grade material is for laboratory use only.
References
- Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-hormone-receptor agonist retatrutide for obesity — a Phase 2 trial. N Engl J Med. 2023;389(6):514–526.
- Rosenstock J, Frías J, Jastreboff AM, et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial conducted in the USA. Lancet. 2023;402(10401):529–544.
This article is provided for educational and research purposes only. Retatrutide is an investigational research compound. It is not an approved drug or therapeutic agent and is not intended for human consumption, diagnosis, treatment, cure, or prevention of any disease or condition. All work involving this peptide should be conducted by qualified personnel within an appropriate research setting and in compliance with applicable institutional and regulatory requirements.