The body uses several hormones to manage food, fuel and body weight. Retatrutide was designed to activate the receptors for three of them at once, and it is now in late-stage human trials.
Retatrutide · Triple-receptor metabolic peptide
After a meal, the gut and pancreas release hormones that tell the body how to handle the fuel arriving: how much insulin to make, how full to feel, how fast to burn stored energy. Researchers ask what happens when several of those signals are switched on together. Retatrutide was built to ask that question, and the evidence is now from human trials in adults with obesity or type 2 diabetes.
Retatrutide, development code LY3437943, is a single synthetic peptide engineered by Eli Lilly to act as an agonist, a molecule that activates a receptor, at three receptors at once. Each receptor normally answers to a different hormone. GLP-1 (glucagon-like peptide-1) is released by the gut after eating and is involved in insulin release, slower stomach emptying and the feeling of fullness. GIP (glucose-dependent insulinotropic polypeptide) is another gut hormone that also prompts insulin release and acts on fat tissue. Glucagon is a pancreatic hormone that raises blood glucose between meals and is associated with increased energy expenditure.
A fatty-acid chain attached to the peptide slows its clearance, giving it a half-life of several days. In cell assays it activates the GLP-1 and glucagon receptors with roughly balanced potency and the GIP receptor more strongly, as described in the discovery paper.
The published human evidence is in adults with obesity or type 2 diabetes, given subcutaneous injections, with body weight or glycated haemoglobin (HbA1c, a three-month average of blood glucose) as the main measures.
A 48-week phase 2 trial in 338 adults with obesity, but without diabetes, reported mean weight change of about 17% to 24% across the higher dose groups against about 2% with placebo; gastrointestinal side effects and a rise in heart rate were dose-related (Jastreboff et al., 2023). A substudy of that trial measured liver fat by MRI in participants with metabolic dysfunction-associated steatotic liver disease (Sanyal et al., 2024).
Phase 3 results began to appear in 2026. TRANSCEND-T2D-1, a 40-week placebo-controlled trial in 537 adults with type 2 diabetes, reported larger HbA1c and weight reductions than placebo and was published in The Lancet. The sponsor has announced topline results from the TRIUMPH obesity trials: TRIUMPH-1 (2,339 adults with obesity or overweight, 80 weeks, placebo comparator) and TRIUMPH-2 and TRIUMPH-3 (adults with type 2 diabetes, and adults with severe obesity and cardiovascular disease). Those figures come from company announcements and had not been published in a peer-reviewed journal at the time of writing.
Whether activating three receptors produces a different result from two is a hypothesis under test, not a settled finding. No published trial has compared retatrutide directly with tirzepatide or semaglutide, so the size of any difference between them is unknown.
All human data come from trials of a pharmaceutical formulation given under medical supervision, with sponsor funding. Topline percentages are reported before independent review, and long-term safety, weight maintenance after stopping, and effects in populations outside the trial criteria have not been described. Material sold for research is not the formulation used in those trials.
Retatrutide is an investigational compound. It is not an approved medicine in Australia and has not been approved by any regulator; phase 3 trials are ongoing and the sponsor has said it plans to apply for US approval in early 2027.
Sources and status checked 2026-09-22
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