What TRIUMPH-1 Reported
On 21 May 2026, Eli Lilly reported topline results from TRIUMPH-1, the pivotal Phase 3 obesity trial for retatrutide (LY3437943) and the first Phase 3 efficacy readout in the TRIUMPH programme. The trial randomised 2,339 adults with obesity, or overweight with at least one weight-related comorbidity, and without type 2 diabetes, to retatrutide 4mg, 9mg, or 12mg once weekly (titrated upward from 2mg in four-weekly steps) or placebo. The primary endpoint was mean percentage change in body weight at 80 weeks.
| Dose cohort | Mean weight loss at 80 weeks | AE-driven discontinuation |
|---|---|---|
| Placebo | 2.2% | ~4.9% |
| 4mg/week | 19.0% | ~4.1% |
| 9mg/week | 25.9% | ~6.9% |
| 12mg/week | 28.3% | ~11.3% |
In a higher-BMI subgroup (n≈532) escalated to the maximum tolerated dose, mean weight reduction reached −30.3% (−38.5 kg; −85.0 lbs) by week 104. The dose-response gradient, more weight loss at higher doses, held at scale across a larger population and a longer endpoint than the Phase 2 trial, while adverse-event-driven discontinuation also rose with dose, consistent with the dose-dependent gastrointestinal profile of the GLP-1 class.
Lilly's disclosure also reported categorical responder rates and absolute weight change at the 80-week endpoint, which sharpen the picture beyond the mean:
| Dose cohort | Mean change (% / kg / lb) | ≥25% weight loss | ≥30% weight loss |
|---|---|---|---|
| Placebo | −2.2% (−2.5 kg; −5.5 lbs) | 2.2% | 0.5% |
| 4mg/week | −19.0% (−21.4 kg; −47.2 lbs) | 27.8% | 15.3% |
| 9mg/week | −25.9% (−29.2 kg; −64.4 lbs) | 52.9% | 37.9% |
| 12mg/week | −28.3% (−31.9 kg; −70.3 lbs) | 62.5% | 45.3% |
At the top dose, a majority of participants (62.5%) lost at least a quarter of their body weight and nearly half (45.3%) lost at least 30%, a responder profile the mean alone does not convey.
These figures are drawn from Eli Lilly's 21 May 2026 topline disclosure (investor.lilly.com) and contemporaneous reporting in the Pharmaceutical Journal. The full peer-reviewed publication and the remaining TRIUMPH readouts are still pending. Retatrutide is supplied by RetaLABS for laboratory research use only and is not approved as a therapeutic in Australia.
Trial Design at a Glance
| Parameter | Value |
|---|---|
| Trial | TRIUMPH-1 (NCT05929066) |
| Phase / design | Phase 3, randomised, double-blind, placebo-controlled |
| Enrolment | 2,339 adults |
| Population | Obesity, or overweight + ≥1 weight-related comorbidity; without type 2 diabetes |
| Arms | Retatrutide 4mg / 9mg / 12mg weekly, or placebo |
| Titration | Upward from 2mg in four-weekly steps to assigned maintenance dose |
| Primary endpoint | Mean % change in body weight at 80 weeks |
| Higher-BMI subgroup | n≈532 escalated to maximum tolerated dose; up to ~30% mean reduction by week 104 |
The 80-week primary endpoint is notably longer than the retatrutide Phase 2 trial's 48-week endpoint, and the four-weekly titration is more gradual than the compressed escalation used in Phase 2, both design choices that affect how the headline percentages should be read against earlier data.
How It Compares (Cross-Trial Context)
The table below places the TRIUMPH-1 12mg result alongside the retatrutide Phase 2 trial and the pivotal obesity trials for tirzepatide and semaglutide. These are cross-trial, observational comparisons, not head-to-head trials. The studies differ in population, duration, dose schedule and design, so direct ranking is not statistically supportable from these figures.
| Trial | Compound | Highest dose | Mean weight loss | Endpoint |
|---|---|---|---|---|
| TRIUMPH-1 (Phase 3) | Retatrutide | 12mg/week | 28.3% | 80 weeks |
| Phase 2 (NEJM 2023) | Retatrutide | 12mg/week | 24.2% | 48 weeks |
| SURMOUNT-1 | Tirzepatide | 15mg/week | 20.9% | 72 weeks |
| STEP 1 | Semaglutide | 2.4mg/week | 14.9% | 68 weeks |
The Phase 3 12mg result (28.3% at 80 weeks) is consistent with the Phase 2 12mg figure (24.2% at 48 weeks, Jastreboff et al., NEJM 2023), now confirmed in a much larger cohort over a longer endpoint. The comparator pivotal trials are SURMOUNT-1 tirzepatide (Jastreboff et al., NEJM 2022) and STEP 1 semaglutide (Wilding et al., NEJM 2021). The mechanistic distinction, retatrutide adds glucagon-receptor agonism to the GLP-1/GIP activity of tirzepatide, is the more defensible comparison axis than any head-to-head percentage ranking. For the full quantified reference, see Retatrutide Statistics 2026; for mechanism and reconstitution, see the Retatrutide Research Guide.
What Is Still Pending
TRIUMPH-1 is the first of several Phase 3 readouts. As of 30 May 2026 the remaining trials have not reported primary endpoint data:
- TRIUMPH-2 (type 2 diabetes with obesity/overweight, NCT05929079), active follow-up.
- TRIUMPH-3 (obesity + cardiovascular disease, NCT05882045), active enrolment, with the University of Sydney Boden Initiative listed as an Australian site; readout anticipated late 2026 to mid-2027.
- TRIUMPH-4 (obesity + knee osteoarthritis, NCT05931367), active enrolment.
- TRIUMPH-Outcomes (cardiovascular outcomes MACE, ~10,000 participants, NCT06383390), longer timeline through 2028.
The peer-reviewed TRIUMPH-1 publication is also still pending; the figures above are from the sponsor's topline disclosure and contemporaneous medical-press reporting. This page will be updated within 14 days of the peer-reviewed publication per the RetaLABS Research Team update policy.