What Is Retatrutide? Definition and What Research Reports

Plain-language definition

Retatrutide is the name of an investigational peptide drug that is injected under the skin once a week and acts on three different hormone receptors in the body at the same time. Those receptors normally respond to the natural gut and pancreas hormones GIP, GLP-1 and glucagon, which together influence appetite, insulin release and energy expenditure. Because it engages three targets rather than one, retatrutide is often described in the literature as a "triple agonist" or "triple-hormone-receptor agonist." It has been tested in clinical trials for obesity and type 2 diabetes, and as of the publications summarised here it remained an investigational compound rather than an approved product.

This page is for educational purposes only and is not medical advice; consult a licensed physician about any medical or health decision. Nothing here describes how a person should use any compound.

What retatrutide is in biochemical terms

Retatrutide is a synthetic, single-chain peptide engineered from the glucagon-peptide family. Its backbone is modified with a fatty-acid chain (lipidation) that extends its half-life enough to support once-weekly subcutaneous administration. The molecule was designed so that one sequence binds and activates three related class B G-protein-coupled receptors:

• GIP receptor — glucose-dependent insulinotropic polypeptide receptor.
• GLP-1 receptor — glucagon-like peptide-1 receptor, the target of several marketed incretin medicines.
• Glucagon receptor — the addition that distinguishes retatrutide from dual GIP/GLP-1 agonists; glucagon receptor activity has been discussed in the literature in relation to energy expenditure and hepatic fat handling.

The discovery and early clinical characterisation of the molecule were published under its development code LY3437943, described as a novel triple glucagon, GIP and GLP-1 receptor agonist taken from discovery through clinical proof of concept (PMID 35985340). A phase 1b multiple-ascending-dose trial in people with type 2 diabetes was also published under the LY3437943 designation (PMID 36354040). Readers encountering "LY3437943" in older papers and "retatrutide" in newer ones are looking at the same compound.

Regulatory status of the term

"Retatrutide" is an International Nonproprietary Name assigned to an investigational agent. Across the published record summarised on this page, the compound was evaluated in randomised trials rather than marketed as an approved therapy. A design paper described the TRIUMPH programme of registrational clinical trials evaluating retatrutide for obesity, obstructive sleep apnoea and knee osteoarthritis, which is the kind of programme conducted to support a regulatory submission (PMID 41090431). Material sold online under this name is not an approved medicine, and peptides labelled "research use only" are, by that label, not intended for human administration. This is not legal advice.

How the term is used in research

In the peer-reviewed literature, "retatrutide" appears almost exclusively as the name of the clinical-trial compound in metabolic medicine. Typical usages include:

• As a study drug in randomised, double-blind, placebo-controlled phase 1, 2 and 3 trials.
• As a comparator concept in reviews of incretin pharmacology — for example, a narrative review framed it as "a game changer in obesity pharmacotherapy" (PMID 40563436) and another as "the power of three" in obesity and diabetes therapy (PMID 39515565).
• As the intervention in systematic reviews and meta-analyses pooling randomised controlled trials (PMID 40291085, PMID 39318607).

Where the term is misused

• Called a "GLP-1" as if that were the whole story. Retatrutide is a triple agonist; describing it only as a GLP-1 drug omits the GIP and glucagon receptor components that define it (PMID 35985340).
• Treated as interchangeable with tirzepatide or semaglutide. Those are different molecules with different receptor profiles and different regulatory histories.
• Described as "approved" or as a treatment. The registrational trial programme was still being described in design papers (PMID 41090431).
• Grouped with "research peptides" like BPC-157 or CJC-1295. Retatrutide has a substantial randomised human trial record; most grey-market peptides do not.
• Trial dose levels quoted as though they were instructions. Doses in published protocols describe what investigators administered under supervision, not a template for anyone else.

Related terms

What the published literature reports

Obesity

A phase 2 randomised trial of retatrutide in adults with obesity was published in 2023 and tested once-weekly subcutaneous doses against placebo over 48 weeks, with body weight change as the primary outcome; the study reported dose-dependent reductions in body weight relative to placebo (PMID 37366315). Systematic reviews and meta-analyses that pooled randomised controlled trials reported consistent weight and metabolic marker changes with once-weekly retatrutide compared with placebo, while noting that the evidence base at that time was drawn from a limited number of trials (PMID 40291085, PMID 39318607).

Type 2 diabetes

A phase 2 trial conducted in the USA evaluated retatrutide in people with type 2 diabetes against both placebo and an active comparator, with glycaemic control among the outcomes; researchers reported reductions in glycated haemoglobin alongside weight reduction (PMID 37385280). A phase 3 trial, TRANSCEND-T2D-1, examined efficacy and safety in people with type 2 diabetes whose glycaemia was inadequately controlled with diet and exercise (PMID 42250575). An earlier phase 1b multiple-ascending-dose study had established initial tolerability and glucose-lowering signals under the LY3437943 name (PMID 36354040).

Body composition and liver fat

A substudy of a phase 2 diabetes trial examined body composition, reporting changes in fat and lean mass among participants receiving retatrutide compared with control (PMID 40609566). A separate randomised phase 2a trial investigated retatrutide in metabolic dysfunction-associated steatotic liver disease and reported reductions in liver fat content relative to placebo (PMID 38858523).

Adverse Events: What Studies Report

Across the published trials, the adverse events most frequently reported were gastrointestinal — nausea, vomiting, diarrhoea and constipation — and these were generally described as dose-related and most common during dose escalation (PMID 37366315, PMID 37385280). Pooled analyses of randomised controlled trials likewise reported a higher incidence of gastrointestinal adverse events with retatrutide than with placebo while assessing overall safety (PMID 40291085). Increases in heart rate were among the cardiovascular observations discussed in the phase 2 obesity trial report (PMID 37366315). Reviews have emphasised that long-term safety remained to be established through the registrational programme (PMID 40563436, PMID 41090431).

Summary of the definition

In short, retatrutide is defined by three things: a peptide structure engineered for weekly subcutaneous dosing, simultaneous agonism at GIP, GLP-1 and glucagon receptors, and an investigational regulatory status supported by a phase 1–3 trial record in obesity and type 2 diabetes. Any use of the word outside that frame — as a marketed drug name, as a synonym for GLP-1 agonists generally, or as a set of instructions — departs from how the published literature uses it.

References

• Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial (The New England Journal of Medicine, 2023)
• Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: Rationale and design of the TRIUMPH registrational clinical trials (Diabetes, Obesity & Metabolism, 2026)
• Retatrutide-A Game Changer in Obesity Pharmacotherapy (Biomolecules, 2025)
• 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 Metabolism, 2022)
• Triple hormone receptor agonist retatrutide for metabolic dysfunction-associated steatotic liver disease: a randomized phase 2a trial (Nature Medicine, 2024)
• 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)
• Effects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2, double-blind, parallel-group, placebo-controlled, randomised trial (The Lancet Diabetes & Endocrinology, 2025)
• The power of three: Retatrutide's role in modern obesity and diabetes therapy (European Journal of Pharmacology, 2024)
• Efficacy and safety of retatrutide, a novel GLP-1, GIP, and glucagon receptor agonist for obesity treatment: a systematic review and meta-analysis of randomized controlled trials (Proceedings (Baylor University Medical Center), 2025)
• Efficacy and safety of retatrutide, a GIP, GLP-1, and glucagon receptor agonist, in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial (Lancet, 2026)
• LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial (Lancet, 2022)
• Effects of once-weekly subcutaneous retatrutide on weight and metabolic markers: A systematic review and meta-analysis of randomized controlled trials (Metabolism Open, 2024)