Key Takeaways
- In the phase 3 TRIUMPH-1 trial, the experimental drug retatrutide produced average weight loss of up to 25.0% over 80 weeks — the largest yet reported for an obesity medicine.
- The drug targets three gut-hormone receptors at once, and also eased knee arthritis pain and sleep apnea in trial subgroups.
- It is not approved anywhere, and its maker has not yet filed for approval.
One Injection, Three Hormones, 25 Per Cent
The weight-loss drug race just produced its biggest number yet. In a phase 3 trial published in the New England Journal of Medicine, people taking the highest dose of an experimental Eli Lilly drug called retatrutide lost an average of 25.0% of their body weight over 80 weeks — roughly 60 pounds for someone starting at 240 pounds — compared with 3.9% on placebo.
The study, called TRIUMPH-1, randomised 2,339 adults with obesity, or overweight with a weight-related condition, to weekly injections of retatrutide at 4, 9 or 12 milligrams, or a placebo. None of the participants had diabetes. Weight loss rose steadily with dose: 17.6% at 4 mg, 23.7% at 9 mg, and 25.0% at 12 mg.
For scale, that top figure is beyond what the current generation of approved drugs achieved in their own trials, and in the range usually associated with bariatric surgery — though cross-trial comparisons are only a rough guide, and no head-to-head trial in this obesity-only population against those treatments exists.
Why Three Targets Instead of One
Retatrutide is nicknamed a "triple agonist" because it switches on three gut-hormone receptors at once. The first, GLP-1, is the target of semaglutide (Ozempic/Wegovy) — it suppresses appetite and slows digestion. The second, GIP, is the added target in tirzepatide (Mounjaro/Zepbound). Retatrutide adds a third: the glucagon receptor, which increases energy expenditure — in effect, pressing the accelerator on calorie burning while the other two press the brake on eating.
The trial also measured two conditions that travel with obesity. Among 574 participants with knee osteoarthritis, pain scores improved substantially more on retatrutide than on placebo. Among 243 with obstructive sleep apnea, the frequency of breathing interruptions — the apnea-hypopnea index — fell far more on the drug. Those are the outcomes that decide whether the benefit is cosmetic or life-changing.
The Costs: Nausea, Strange Skin Sensations, Dropouts
The side-effect profile will be familiar to anyone who has followed this drug class — with one new entry. The most common problems were gastrointestinal: nausea affected up to 42.4% of people on the top dose (versus 14.8% on placebo), alongside diarrhea, constipation and vomiting. A less typical effect, dysesthesia — an abnormal, unpleasant skin sensation — was reported by 12.5% on the highest dose, versus 0.9% on placebo. Researchers will be watching it closely in future studies, especially because it has not been a prominent effect with GLP-1-based drugs.
Tolerability decided who finished: 11.3% of participants on the 12 mg dose needed to stop treatment because of adverse events, versus 4.9% on placebo. The benefits were largest at the dose that is hardest to stay on.
The Honest Part: You Cannot Get This Drug
Retatrutide is not approved by the FDA, Health Canada, or any other regulator — anywhere. Eli Lilly has not yet filed for approval. The company has said it plans to submit in the first quarter of 2027, which places any possible approval well after that, and the trial programme is still running, including a companion study in people with type 2 diabetes that showed smaller — but still substantial — losses.
Two cautions belong in any honest reading of the headline number. The 25.0% figure is the trial's main analysis, covering everyone randomised. A separate "efficacy" analysis limited to people who stayed on treatment produced 28.3% — the number most likely to travel on social media, and the one that flatters the drug most. And an 80-week trial in a selected, closely monitored population cannot yet answer the questions that matter over decades: what happens when people stop, and what rare harms only appear at population scale.
The Twikup Take
Retatrutide is the strongest evidence yet that multi-hormone obesity drugs keep raising the ceiling — 25% average weight loss, with joint pain and sleep apnea improving alongside. But today it is a result, not a treatment. The most powerful obesity drug in the world right now is one nobody can be prescribed.
This article is general information about a clinical study, not medical advice. Talk to your own clinician about weight-management options that are approved and available in Canada.
Image: Illustrative image.