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 | 3.9% | ~4.9% |
| 4mg/week | 17.6% | ~4.1% |
| 9mg/week | 23.7% | ~6.9% |
| 12mg/week | 25.0% | ~11.3% |
In a higher-BMI subgroup (n≈532) escalated to the maximum tolerated dose, mean weight reduction reached up to ~30% 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.
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 (NCT05882045) |
| 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 | 25.0% | 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 (25.0% 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 (obesity + sleep apnoea, NCT05882049) — active follow-up.
- TRIUMPH-3 (obesity + cardiovascular disease, NCT05882077) — active enrolment, with the University of Sydney Boden Initiative listed as an Australian site; readout anticipated late 2026 to mid-2027.
- TRIUMPH-4 (adolescent obesity, NCT05989711) — active enrolment.
- SYNERGY-OUTCOMES (cardiovascular outcomes MACE, ~17,000+ participants, NCT06077864) — longer timeline through 2028.
- TRIUMPH-NAFLD (MASH/MASLD, NCT06324877) — active enrolment.
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.