Retatrutide (LY3437943) is a single synthetic peptide that simultaneously activates three metabolic receptors: the glucose-dependent insulinotropic polypeptide receptor (GIPR), the glucagon-like peptide-1 receptor (GLP-1R), and the glucagon receptor (GCGR). This triple-agonist design is what distinguishes it from single-receptor agonists such as semaglutide and dual GIP/GLP-1 agonists such as tirzepatide. Developed by Eli Lilly, retatrutide is an investigational compound — it is not approved by any regulator and is supplied here for laboratory research use only. This page summarises its receptor pharmacology and structural basis, with references to the primary literature.
Why three receptors?
Each of the three receptors contributes a distinct arm to energy balance, and the design rationale is that engaging all three produces a broader metabolic profile than any single- or dual-receptor agonist. In the preclinical characterisation by Coskun and colleagues (Cell Metabolism, 2022), the molecule showed balanced glucagon- and GLP-1-receptor activity with comparatively more prominent GIP-receptor activity, and in obese animal models glucagon-receptor engagement added an energy-expenditure component layered on top of the appetite- and glucose-related effects driven by the GIP and GLP-1 arms.
Receptor by receptor
The most established incretin target; GLP-1R agonism underlies the pharmacology of semaglutide and contributes to glucose-dependent insulin secretion and appetite signalling. This is the shared arm across the whole incretin class.
The second incretin axis. In the retatrutide binding profile this arm is comparatively prominent. GIP biology is more contested in the literature than GLP-1 biology; see Hammoud & Drucker (Nature Reviews Endocrinology, 2023) for the contrasting cardiometabolic actions of GIP and GLP-1.
The distinguishing arm. Adding glucagon-receptor agonism to an incretin agonist is sometimes described as a paradox, because glucagon classically raises blood glucose. The design intent is that GCGR-driven increases in energy expenditure are offset by the glucose-lowering incretin arms, so the net metabolic direction is maintained while an additional energy-expenditure mechanism is recruited.
Structure
Retatrutide is a synthetic peptide engineered from a GIP-based backbone with several non-coded residue substitutions and a C20 fatty-diacid side chain. The fatty-diacid moiety promotes albumin binding, which extends the circulating half-life and supports once-weekly dosing in the clinical programme. The molecular weight is approximately 4,731 Da. Structural specifics are reported as stated in the primary Coskun 2022 characterisation.
Receptor targets across the incretin class
| Compound | GLP-1R | GIPR | GCGR | Class | Regulatory status |
|---|---|---|---|---|---|
| Semaglutide | ✔ | — | — | GLP-1 mono-agonist | Approved |
| Tirzepatide | ✔ | ✔ | — | GIP/GLP-1 dual agonist | Approved |
| Retatrutide (LY3437943) | ✔ | ✔ | ✔ | GIP/GLP-1/glucagon triple agonist | Investigational — not approved |
For a fuller side-by-side of structure, half-life, and development stage, see how retatrutide differs from tirzepatide and semaglutide.
What the clinical literature reports
Reported strictly as published, attributed clinical findings — not as product claims. A Phase 2 obesity trial (Jastreboff et al., NEJM, 2023) and a Phase 2 type 2 diabetes trial (Rosenstock et al., Lancet, 2023) reported the compound’s metabolic effects; a Phase 2a trial in metabolic-dysfunction-associated steatotic liver disease (Nature Medicine, 2024) reported reductions in liver fat. Phase 3 registrational trials are ongoing. Retatrutide remains investigational and is not approved for clinical use.
Open questions
A strong research page names what is not yet settled: the long-term durability of effect, the full characterisation of glucagon-receptor engagement in humans, weight trajectory after discontinuation, and the relative contribution of each receptor arm to the overall profile all remain active areas of investigation. Acknowledging this uncertainty is both accurate and, we think, the honest way to write about an investigational compound.
References
- Coskun T, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: from discovery to clinical proof of concept. Cell Metab. 2022;34(9):1234–1247. doi:10.1016/j.cmet.2022.07.013
- Rosenstock J, 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. Lancet. 2023;402(10401):529–544. doi:10.1016/S0140-6736(23)01053-X
- Jastreboff AM, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023;389(6):514–526. doi:10.1056/NEJMoa2301972
- Sanyal AJ, et al. Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial. Nat Med. 2024;30(7):2037–2048. doi:10.1038/s41591-024-03018-2
- Hammoud R, Drucker DJ. Beyond the pancreas: contrasting cardiometabolic actions of GIP and GLP1. Nat Rev Endocrinol. 2023;19(4):201–216. doi:10.1038/s41574-022-00783-3
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