Retatrutide is an experimental once-weekly injection from Eli Lilly. It acts on three hormone receptors at once — GLP-1, GIP and glucagon — and has produced the largest weight loss ever reported in a trial. It is not approved in any country and cannot be prescribed.
The short version
| What it is | An experimental weekly injection for obesity and type 2 diabetes |
| Also called | LY3437943 |
| Maker | Eli Lilly |
| Status | Not approved anywhere. In phase 3 trials |
| How it works | Activates the GLP-1, GIP and glucagon receptors together |
| Best result | 24.2% mean weight loss at 48 weeks (phase 2) |
| Can you get it? | No, except through a narrow compassionate use programme |
Why three receptors instead of one
The drugs already approved work on one or two targets. Semaglutide — Ozempic and Wegovy — activates GLP-1 alone. Tirzepatide, in Mounjaro and Zepbound, adds GIP, and produces more weight loss as a result.
Retatrutide adds a third: glucagon. That one is counter-intuitive, because glucagon raises blood sugar on its own. But it also increases how much energy the body spends and helps break down stored fat. Paired with two receptors that lower blood glucose, the sugar-raising effect is offset while the metabolic effect is kept.
Put simply: the first two receptors reduce how much you eat, and the third increases how much you burn. Every approved drug in this class works only on the first half of that equation.
What the trials found
In obesity, a 338-person trial published in 2023 found 24.2% mean weight loss at 48 weeks on the highest dose, against 2.1% on placebo. Every participant on the top two doses lost at least 5% of their body weight, and 83% of the highest-dose group lost at least 15%.
In type 2 diabetes, the first phase 3 trial reported in 2026: 15.3% weight loss and an HbA1c reduction of 1.94% at 40 weeks, in 537 people. Weight loss is always lower in this population, and 15.3% still exceeded what approved drugs achieve there over longer trials.
For scale, semaglutide reaches about 14.9% and tirzepatide about 20.9% in obesity. The full figures are in retatrutide weight loss.
Can you take it? No
This is the part that matters most and it is usually mentioned last.
Retatrutide has not been approved by the FDA, the EMA or any other regulator. No doctor can prescribe it and no pharmacy can dispense it. The only legitimate route is a narrow compassionate use programme, reported in 2026, intended for individual patients with serious conditions and no remaining options.
It is nonetheless sold online as a "research peptide". In 2026 researchers analysed three such products in Australia, all labelled 10 mg. All three contained genuine retatrutide and were free of significant metal contamination — but held 51%, 165% and 190% of the labelled dose. Nearly four-fold variation between vials that look identical. Since every side effect in the trials was dose-related, that variation is the problem, not the molecule. More in can you buy retatrutide.
When might it be available?
There is no approval date. Retatrutide is in phase 3 with fourteen registered trials, several still active, including a 10,000-patient study of cardiovascular outcomes. A company files after its pivotal trials report, and a regulator then takes its own time. Any specific date circulating is a projection.
What can be tracked is progress, and it is in the GLP-1 pipeline tracker alongside every other molecule in development.
Where to go next
The full retatrutide guide covers both trials, the phase 3 programme and the safety findings. If you are comparing it with what you can actually get, see retatrutide vs Zepbound and retatrutide vs Wegovy. And if the effect is what you want from something available now, the approved options are ranked in the best GLP-1 for weight loss.
Scientific References
3 sources- 1
Jastreboff AM, Kaplan LM, Frías JP, et al.
Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial
New England Journal of Medicine · 389(6) · 2023PMID: 37366315
NEJM - 2
Bajaj HS, Welch M, Shah P, et al.
Efficacy and safety of retatrutide in people with type 2 diabetes (TRANSCEND-T2D-1): a phase 3 trial
The Lancet · 407(10546) · 2026PMID: 42250575
- 3
Piatkowski T, Craven A, Cornell S, Ferris J
Composition and Labelling Accuracy of Products Sold as Retatrutide in Australia
Drug and Alcohol Review · 45(6) · 2026PMID: 42559975
NIH
References open in a new tab. Content is reviewed against peer-reviewed literature as part of our editorial policy.
About the author
Editor, Modern Weight Science
Claudiu Gheorghe is the editor of Modern Weight Science. He is not a physician. His role is to synthesize peer-reviewed studies, clinical-trial data, and FDA prescribing information into clear, plain-language explanations, and to make sure every factual claim on the site traces back to a cited source. Any decision about starting, changing, or stopping a medication belongs with a licensed clinician who knows your history.
Every claim is checked against peer-reviewed research through our review process and fact-checking policy.
Frequently Asked Questions
What is retatrutide?
An experimental once-weekly injection developed by Eli Lilly, known in trials as LY3437943. It activates three hormone receptors at once — GLP-1, GIP and glucagon — where approved drugs like Ozempic and Zepbound use one or two. It is in phase 3 trials and is not approved in any country.
Is retatrutide approved by the FDA?
No. It is not approved by the FDA, the EMA or any other regulator, so no doctor can prescribe it and no pharmacy can dispense it. The only legitimate route is a narrow compassionate use programme reported in 2026, which is intended for individual patients with serious conditions and no other options.
How much weight loss does retatrutide cause?
In its phase 2 trial, 24.2% mean weight loss at 48 weeks on the highest dose, against 2.1% on placebo — the largest figure reported for any weight-loss drug. Every participant on the top two doses lost at least 5% of body weight. In the first phase 3 trial, in people with type 2 diabetes, it was 15.3% at 40 weeks.
Why does retatrutide work on three receptors?
Because they do different jobs. GLP-1 and GIP reduce appetite; glucagon increases how much energy the body spends and helps break down stored fat. Glucagon raises blood sugar on its own, but pairing it with two receptors that lower blood glucose offsets that while keeping the metabolic effect. Every approved drug in this class works only on the intake side.
When will retatrutide be available?
There is no approval date. It is in phase 3 with fourteen registered trials, several still running, including a 10,000-patient cardiovascular outcomes study. A manufacturer files after its pivotal trials report and a regulator then takes its own time, so any specific date in circulation is a projection rather than a schedule.
Is the retatrutide sold online real?
Chemically, often yes — and that is not the problem. Three products sold in Australia and labelled 10 mg were analysed in 2026: all three contained genuine retatrutide with no significant metal contamination, but held 51%, 165% and 190% of the labelled dose. Since every side effect in the trials was dose-related, a vial whose strength varies four-fold is a dosing problem regardless of whether the molecule inside is authentic.
Continue learning
Where to read next
Not medical advice. This guide is for general education only. GLP-1 medications, dosing, and treatment suitability are decisions for you and a licensed clinician who knows your full medical history.