TRIUMPH-1: retatrutide's main obesity trial explained
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TRIUMPH-1 is the largest retatrutide trial to report so far and the one most of the headlines come from. Lilly announced topline results on 21 May 2026 and presented more detail at the American Diabetes Association meeting in June. The peer-reviewed paper has not been published yet.
What the trial did
Participants were assigned at random to one of four groups. Everyone in the retatrutide groups began on a low dose, and the trial stepped the dose up every four weeks until they reached their assigned target. That stepped approach is a standard trial design for this drug class, used to reduce nausea early on. The exact schedule is a design detail of the trial; it is not a template for anything outside it.[1]
TRIUMPH-1 was also a "basket" trial: nested inside it were smaller groups with moderate-to-severe obstructive sleep apnoea and with knee osteoarthritis, each with their own outcome measures.[3]
Weight loss
| Group | Treatment-regimen estimand (all randomised) | Efficacy estimand (on treatment) |
|---|---|---|
| Retatrutide 4 mg | −17.6% | −19.0% |
| Retatrutide 9 mg | −23.7% | −25.9% |
| Retatrutide 12 mg | −25.0% | −28.3% |
| Placebo | −3.9% | −2.2% |
Figures at 80 weeks.[1] The two columns are explained in how to read a trial.
Other results at 80 weeks:
- Big losses were common on the higher doses. 62.5% of the 12 mg group lost at least 25% of their body weight, and 45.3% lost at least 30%. On placebo the figures were 2.2% and 0.5%.
- BMI thresholds. 65.3% of people on 12 mg finished with a BMI under 30, including 37.5% of those who started with a BMI of 40 or more.
- Waist: down 9.5 inches (about 24 cm) on 12 mg versus 1.4 inches on placebo.
- Risk markers: improvements in non-HDL cholesterol, triglycerides, systolic blood pressure and the inflammation marker hs-CRP.
- Sleep apnoea sub-group: breathing interruptions fell by up to 36.1 events per hour, a 60.6% reduction from a starting average of 58.6.[4]
The 104-week extension
People who started with a BMI of 35 or higher could continue for a further 24 weeks. In that group, average loss on the 12 mg arm reached 30.3% at 104 weeks on the efficacy estimand (29.9% on the treatment-regimen estimand).[1]
The extension group is a subset, chosen because they had the most weight to lose, and people who had already done well were more likely to continue. The 30.3% figure is real, but it is not "what retatrutide does over two years" for everyone. It is what happened in the heaviest participants who stayed in.
Side effects and drop-outs
| Event | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Nausea | 28.6% | 38.4% | 42.4% | 14.8% |
| Diarrhoea | 25.2% | 34.1% | 32.0% | 13.5% |
| Constipation | 23.8% | 25.9% | 26.1% | 10.9% |
| Vomiting | 10.6% | 22.8% | 25.3% | 4.8% |
| Dysesthesia (altered skin sensation) | 5.1% | 12.3% | 12.5% | 0.9% |
| Upper respiratory tract infection | 14.2% | 12.2% | 13.1% | 11.6% |
| Urinary tract infection | 7.5% | 8.8% | 8.4% | 5.3% |
| Stopped treatment because of side effectsAny adverse event leading to discontinuation | 4.1% | 6.9% | 11.3% | 4.9% |
Gastrointestinal effects dominated and were mostly mild to moderate, concentrated during dose escalation. Dysesthesia, an altered skin sensation such as tingling or heightened sensitivity, appeared in up to 12.5% of participants; it is a new finding in Phase 3 and is covered on its own page. More people stopped on the higher doses, though the 4 mg drop-out rate was below placebo.[1] See discontinuation rates.
Lilly's announcement did not report heart rate changes or arrhythmia rates. Those will matter when the full paper appears, because a heart-rate rise was seen in Phase 2. See heart rate and rhythm.
What is still unknown from this trial
- The full peer-reviewed paper, with heart-rate, rhythm, liver and pancreas data by dose.
- What happened to weight after the trial ended. A separate maintenance trial (TRIUMPH-6) is running.
- Longer-term effects beyond two years, and effects in people excluded from the trial.
References
- Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial (TRIUMPH-1 topline results). Eli Lilly and Company, press release, 21 May 2026. Primary source
- TRIUMPH-1: A Study of Retatrutide in Participants With Obesity or Overweight Without Type 2 Diabetes (NCT05929066). ClinicalTrials.gov, 6 April 2026. Primary source
- Giblin K, Kaplan LM, Somers VK, et al. Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: Rationale and design of the TRIUMPH registrational clinical trials. Diabetes, Obesity and Metabolism (doi:10.1111/dom.70209), 15 October 2025. Primary source
- Lilly's triple agonist, retatrutide, drove substantial improvements in weight, A1C, knee osteoarthritis pain, and obstructive sleep apnea (ADA 86th Scientific Sessions presentation). Eli Lilly and Company, press release, 6 June 2026. Primary source