TRIUMPH-1 Decoded: 24% Weight Loss at 48 Weeks
TRIUMPH-1 delivered ~24% weight loss for retatrutide at 48 weeks. Here's the dose-response breakdown and how it compares to STEP and SURMOUNT data.
May 18, 2026 · 7 min read · By GLP-FAQ Editors
The headline from TRIUMPH-1 retatrutide data: approximately 24% mean weight loss at 48 weeks at the highest dose. That number is larger than tirzepatide's SURMOUNT-1 result (~21% at 72 weeks) and considerably larger than semaglutide's STEP-1 result (~15% at 68 weeks). Before it gets carried as a simple comparison, it's worth understanding what it actually measures — and what it doesn't.
What TRIUMPH-1 Is
The TRIUMPH program (Triple hormone Receptor agoNIsm for People with obesity and coMorbidities with High cardiovascular risk) is Eli Lilly's Phase 3 development program for retatrutide (LY3437943), a triple agonist targeting the GLP-1, GIP, and glucagon receptors simultaneously.
TRIUMPH-1 is the core obesity cohort: adults with BMI ≥ 30, or BMI ≥ 27 with a weight-related comorbidity, without type 2 diabetes. It's structured to mirror STEP-1 and SURMOUNT-1 as closely as possible — same-ish population, same primary endpoint (percent weight change from baseline), similar duration — so that the results are at least roughly comparable across programs.
The foundational data behind the 24% figure comes from the Phase 2 trial published by Jastreboff et al. in the New England Journal of Medicine in 2023, which enrolled 338 adults and ran five dose arms over 48 weeks. TRIUMPH-1 Phase 3 subsequently confirmed the Phase 2 signal at scale, with topline data showing results consistent with the Phase 2 highest-dose arm.
Understanding both trials — Phase 2 for depth, Phase 3 for generalizability — is the right frame for reading the data.
The Dose-Response Curve: 24% Is the Ceiling
The retatrutide 24 percent figure is not the average across all treated participants. It's the result at the highest dose studied (12 mg weekly), and it represents the top of a steep dose-response curve.
In the Phase 2 trial, weight loss at 48 weeks broke down roughly as follows:
| Dose | Mean weight loss at 48 weeks |
|---|---|
| Placebo | ~2.1% |
| 1 mg | ~8.7% |
| 4 mg | ~17.3% |
| 8 mg | ~22.8% |
| 12 mg | ~24.2% |
Two things stand out. First, even at 4 mg, retatrutide produced weight loss (~17%) that exceeds semaglutide's headline STEP-1 result. Second, the curve flattens between 8 mg and 12 mg — the 12 mg dose adds roughly 1.4 percentage points over 8 mg, a modest increment at the top of the range.
What this means practically: many people in clinical practice will titrate to 8 mg rather than 12 mg depending on tolerability — and they'd still be looking at ~23% weight loss. The dose-response data is arguably more impressive at the 4–8 mg range, where the gains per milligram are larger, than at the headline 12 mg ceiling.
Phase 3 data is expected to show a similar curve, though the exact percentages may shift somewhat with a larger, more heterogeneous sample.
Mean vs. Median: Reading the Distribution
Trial reports lead with the mean, but the distribution around that mean tells you more.
In the Phase 2 retatrutide high-dose arms, the responder analysis was notably favorable:
- Roughly 90%+ of participants in the 8 mg and 12 mg arms lost at least 5% of body weight
- Around 80% lost at least 10%
- Around 60–65% lost at least 20% — crossing what has historically been considered near-bariatric territory
Compare this to STEP-1 semaglutide, where roughly 69% lost ≥10% and 32% lost ≥20%. The shift in the 20%+ responder rate is meaningful — retatrutide appears to move more people into the high-responder tier.
The key question is whether this distribution reflects the mean alone (pulled up by outliers) or a genuine shift of the whole distribution. The data points toward the latter: the median and mean are close, suggesting the average isn't being propped up by a small cluster of exceptional responders. A true population-level shift.
That said, a non-responder tail remains. Roughly 10–15% of participants in the highest-dose arms lost less than 5%. The predictors of non-response haven't been fully characterized yet.
Comparison to STEP-1 and SURMOUNT-1
This is where the triumph trial weight loss data looks most dramatic — and where the caveats matter most.
| Trial | Drug | Highest dose | Duration | Mean weight loss |
|---|---|---|---|---|
| STEP-1 (2021) | Semaglutide | 2.4 mg | 68 weeks | ~14.9% |
| SURMOUNT-1 (2022) | Tirzepatide | 15 mg | 72 weeks | ~20.9% |
| Retatrutide Phase 2 (2023) | Retatrutide | 12 mg | 48 weeks | ~24.2% |
The apparent advantage for retatrutide is real, but the comparison is not clean for several reasons.
Duration mismatch. STEP-1 and SURMOUNT-1 ran 68–72 weeks; Phase 2 retatrutide ran 48 weeks. Weight loss on GLP-1 agents typically plateaus at around 40–50 weeks for most participants, so you're likely capturing near-peak results for all three — but the extra 20+ weeks in the longer trials also give more time for dropouts, adverse events, and plateau effects to pull the mean down. This modestly favors retatrutide's shorter-duration result.
Trial-generation effect. STEP-1 enrolled in 2018–2019. SURMOUNT-1 in 2020–2021. Retatrutide Phase 2 in 2021–2022. Each successive generation of obesity trials tends to enroll participants with better metabolic health and higher adherence — partly because awareness of GLP-1s brings more motivated participants to trials. This incremental bias is hard to quantify but plausibly accounts for 1–2 percentage points of the retatrutide advantage.
Phase 2 vs. Phase 3 dynamics. Phase 2 trials involve closer monitoring, more frequent contact with clinical staff, and typically better adherence. Phase 3 numbers are usually more conservative. TRIUMPH-1's Phase 3 confirmation showed results consistent with Phase 2 at the highest dose, which is encouraging — but the full publication will clarify how the numbers shifted at scale.
None of this erases retatrutide's likely advantage. The signal is consistent, the biology supports it (the glucagon arm adds a metabolic-rate mechanism that dual-agonists don't have), and the distribution analysis shows a genuine shift rather than a statistical artifact. The question is magnitude — whether the true head-to-head advantage over tirzepatide is 3 percentage points or 5 percentage points or something else.
Why Adding Glucagon Changes the Math
Semaglutide and tirzepatide reduce body weight primarily by suppressing intake. They lower appetite, slow gastric emptying, and reduce the drive to eat. Those mechanisms are real and effective.
Retatrutide adds glucagon receptor agonism — a mechanism that operates partly independently of intake. Glucagon stimulates thermogenesis in brown adipose tissue and promotes fat mobilization. In plain terms: it raises your metabolic rate and shifts your body toward burning stored fat, independent of whether you've eaten less.
The theoretical advantage is that you're working two separate levers simultaneously: eat less (GLP-1 + GIP) and burn more (glucagon). This could partly explain why the highest retatrutide doses exceed what titrating higher doses of dual-agonists produces — you're not just getting more appetite suppression, you're getting a different type of effect on top.
The tradeoff is that glucagon receptor activation comes with real tolerability costs: higher nausea rates and some acceleration of resting heart rate. Whether that trade is worth it for a given individual depends heavily on how they tolerate the titration period.
Tolerability: The Other Side of the Number
The 24% figure comes with a higher side-effect load than semaglutide or tirzepatide at their respective maintenance doses. In Phase 2:
- Nausea was reported in ~40–50% of participants in the high-dose arms, mostly mild to moderate and concentrated in the titration period
- Vomiting rates were higher than what's typically seen with tirzepatide at matched weight-loss doses
- Discontinuation for adverse events ran roughly 10–16% in the 8–12 mg arms
Resting heart rate increased modestly across the dose range — a glucagon effect — which will be watched closely in the cardiovascular outcome data from TRIUMPH-2.
Whether TRIUMPH-1's refined titration protocol improved tolerability vs. Phase 2 is one of the things to look for in the full publication.
What the Full TRIUMPH-1 Readout Will Add
The topline data confirms the headline. What the full publication will add:
- Body composition breakdown (lean mass vs. fat mass preserved — especially important given the glucagon arm's theoretical muscle-preservation effects)
- Responder/non-responder predictors
- 52-week and extension cohort data
- Full adverse event and discontinuation tables
- Subgroup analyses by baseline BMI, sex, and metabolic profile
For context on where retatrutide fits relative to tirzepatide in a matched-population frame, see our retatrutide vs tirzepatide comparison.
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