Retatrutide is the incretin agonist that has delivered the highest weight-loss figures of any molecule in clinical testing. The 2026 phase 3 data reinforced the picture that phase 2 (NEJM 2023) first drew.
Phase 3 (TRIUMPH-1): 28.3% at 80 weeks
On 21 May 2026, Eli Lilly published topline data from TRIUMPH-1— the largest phase 3 trial on retatrutide to date, with 2,339 adult participants. Mean weight reduction: 28.3%at 80 weeks. That 28.3% is a topline result — the headline figure released ahead of full peer-reviewed publication — and TRIUMPH-1 is the lead trial in the broader TRIUMPH phase 3 programme, with secondary endpoints and independent peer review still pending. Treat it as a strong but still-maturing phase 3 signal rather than a sealed evidence package. The weight curve continued downward throughout the study period with no visible plateau. Tolerability was described as consistent with the GLP-1 class: predominantly mild to moderate, gastrointestinal and transient events managed through gradual dose titration. We cover the full safety picture in the retatrutide side-effects review.
Results in context: against tirzepatide and semaglutide
Against the published headline figures for the established molecules, retatrutide’s phase 2 number looks like this:
| Molecule | Study | Weight loss | Timepoint |
|---|---|---|---|
| Semaglutide | STEP-1 | 14.9% | 68 wk |
| Tirzepatide | SURMOUNT-1 | 20.9% | 72 wk |
| Retatrutide | Phase 2 (NEJM) | 24.2% | 48 wk |
| Retatrutide | TRIUMPH-1 (ph. 3) | 28.3% | 80 wk |
Published headline figures per molecule.
Results by dose
The effect is clearly dose-dependent. In the phase 2 study (NEJM 2023), the 12 mg arm reached up to 24.2% weight reduction at 48 weeks, while lower doses produced proportionally lower outcomes. TRIUMPH-1 confirmed the pattern at 80 weeks with 28.3%. The principle is straightforward: higher dose, longer titration, larger observed effect — but individual tolerability is always the limiting factor in clinical research.
Why retatrutide reaches higher numbers
The answer lies in the receptor profile. Retatrutide is a triple agonist — it activates three receptors simultaneously: GLP-1, GIP and glucagon (GCGR). Semaglutide targets one receptor (GLP-1); tirzepatide targets two (GLP-1 and GIP). The glucagon-receptor axis is mechanistically associated with increased energy expenditure on top of the appetite and glycaemic effects delivered by the GLP-1/GIP axis — the rationale most frequently cited in the literature when researchers discuss why retatrutide produces larger effect sizes than its predecessors. More receptors, a broader metabolic signal — but also a more complex balance to optimise. See the differences in receptor profile.
How quickly do results appear?
Not in the first few weeks. The protocol starts with a long up-titration, partly to manage gastrointestinal tolerability — faster dose escalation increases the risk of adverse events. The effect compounds month by month and the peak figures are seen after 48–80 weeks, not 4–8. Because the weight curve was still descending at 80 weeks with no visible plateau, the maximum effect may not have been reached within the studied window. You can map out the full titration schedule in our protocol calculator.
What the literature observes
“Experience” in a research context means observed outcomes, not forum anecdotes. The recurring pattern in the published data is three things: dose-dependent effect, gradual build-up, and gastrointestinal events managed through titration — consistent across the entire incretin class.
What the results do not tell you
Three important limitations to keep in mind. First: the trials for the three molecules (STEP-1, SURMOUNT-1 and TRIUMPH-1) are separate studies with different populations — no direct head-to-head comparison has been published. The numbers are effect sizes within each study, not within the same cohort. The trials also differ in duration: STEP-1 ran for 68 weeks, SURMOUNT-1 for 72 weeks, retatrutide phase 2 for 48 weeks, and TRIUMPH-1 for 80 weeks — a longer study has more time to accumulate effect, which is another reason the raw percentages are not directly comparable. Second: what happens to weight after treatment endsfalls outside the published primary endpoints and remains an open research question. Third: “experiences” circulating outside clinical contexts are anecdotes, not study data — keep them separate.