Overview: a triple agonist
Retatrutide is the non-proprietary name for the compound originally designated LY3437943. It belongs to the same broad family as the well-known GLP-1 medicines — but it is distinguished by acting on three receptor targets rather than one or two. It is administered as a once-weekly subcutaneous injection in the clinical trials that have studied it.
The three targets are the receptors for GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and glucagon. Because one molecule engages all three, retatrutide is described as a "triple agonist" or "triple hormone receptor agonist."
How the triple-agonist mechanism works
Each of the three receptors contributes a different metabolic effect. Activating all three with a single peptide is the design rationale behind retatrutide:
GLP-1 receptor
Slows gastric emptying, increases satiety and supports glucose-dependent insulin release — the core appetite and glucose effect shared with semaglutide and tirzepatide.
GIP receptor
A second incretin pathway thought to complement GLP-1 on insulin secretion and appetite, and the mechanism tirzepatide adds over a pure GLP-1 drug.
Glucagon receptor
The component unique to retatrutide. Glucagon-receptor activity is associated with increased energy expenditure and reduced hepatic (liver) fat in the studied trials.
The glucagon arm is the reason retatrutide is sometimes described as going "one receptor further" than tirzepatide. It is also the component most associated with retatrutide-specific effects, including a transient rise in heart rate observed in the published Phase 2 trial. We cover that in detail in the side-effects article.
How it differs from semaglutide and tirzepatide
The simplest way to place retatrutide is by counting receptors. Each step adds a mechanism the previous generation lacked:
| Compound | Receptors | Status |
|---|---|---|
| Semaglutide (Ozempic / Wegovy) | GLP-1 only | Approved |
| Tirzepatide (Mounjaro / Zepbound) | GLP-1 + GIP | Approved |
| Retatrutide (LY3437943) | GLP-1 + GIP + glucagon | Investigational |
For a full side-by-side of mechanism, trial data and titration, see Retatrutide vs Tirzepatide and Retatrutide vs Semaglutide.
Development status
Retatrutide is being developed by Eli Lilly. The compound progressed through a Phase 2 trial whose weight-loss results were published in the New England Journal of Medicine (Jastreboff et al., 2023; DOI 10.1056/NEJMoa2301972), and into a Phase 3 programme conducted under the TRIUMPH name.
As an investigational compound, retatrutide had not received marketing approval from the MHRA, EMA, FDA or any regulator at the time of writing. Approval timelines for drugs in late-stage trials are uncertain and should be checked against the manufacturer's and regulators' primary announcements rather than assumed. The published trial figures are summarised in the trial-results article.
Frequently asked questions
What is retatrutide in simple terms?
Retatrutide (development code LY3437943) is an investigational once-weekly injectable peptide that activates three gut-hormone receptors at once — GLP-1, GIP and glucagon. It is being studied for weight management and metabolic conditions and is not an approved medicine.
What does 'triple agonist' mean?
An agonist is a molecule that switches a receptor on. Retatrutide is a triple agonist because a single molecule binds and activates three different receptors — GLP-1, GIP and glucagon — rather than one (like semaglutide) or two (like tirzepatide).
Is retatrutide the same as Mounjaro or Ozempic?
No. Ozempic/Wegovy (semaglutide) is a single GLP-1 agonist and Mounjaro (tirzepatide) is a dual GLP-1/GIP agonist; both are approved medicines. Retatrutide adds glucagon-receptor activity as a third mechanism and remains investigational.
Is retatrutide approved or available as a medicine?
No. As of 2026 retatrutide is still in clinical development and is not approved by the MHRA, EMA, FDA or any regulator for human use. It is handled as a research compound only. See our UK legal-status article for detail.
Continue the cluster
Next: the UK legal status, the side-effect profile, and the published trial data.