Retatrutide has produced two headline weight-loss figures: 24.2% at 48 weeks in adults with obesity, and 15.3% at 40 weeks in adults with type 2 diabetes. They are not competing claims and neither supersedes the other. They come from different populations, and the difference between them is the most informative thing about this drug.
Phase 2, in obesity without diabetes
Published in the New England Journal of Medicine in 2023: 338 adults with obesity, or overweight plus a weight-related condition, randomised to one of six retatrutide regimens or placebo for 48 weeks.
| Mean weight change | Placebo | 1 mg | 4 mg | 8 mg | 12 mg |
|---|---|---|---|---|---|
| At 24 weeks | −1.6% | −7.2% | −12.9% | −17.3% | −17.5% |
| At 48 weeks | −2.1% | −8.7% | −17.1% | −22.8% | −24.2% |
The responder figures are the ones worth remembering:
| Proportion who lost | Placebo | 4 mg | 8 mg | 12 mg |
|---|---|---|---|---|
| At least 5% | 27% | 92% | 100% | 100% |
| At least 10% | 9% | 75% | 91% | 93% |
| At least 15% | 2% | 60% | 75% | 83% |
Nobody on 8 mg or 12 mg failed to lose at least 5% of their body weight. Not most of them — all of them. And 83% of the 12 mg group lost at least 15%.
Two caveats belong here. 338 people is a phase 2 trial, small enough that results routinely soften at scale. And 48 weeks is shorter than the 68 to 72 weeks the approved drugs' trials ran, with the curve still descending at the end.
Phase 3, in type 2 diabetes
The first phase 3 trial to report was TRANSCEND-T2D-1, published in the Lancet in June 2026: 537 adults with type 2 diabetes inadequately controlled by diet and exercise alone, over 40 weeks.
| At 40 weeks | Placebo | 4 mg | 9 mg | 12 mg |
|---|---|---|---|---|
| Weight change | −2.6% | −11.5% | −13.9% | −15.3% |
| HbA1c change | −0.81% | −1.69% | −1.86% | −1.94% |
Baseline was a mean age of 48.8, HbA1c of 7.9%, and BMI of 35.8. Nine in ten participants completed the treatment period on drug.
Why 15.3% is the more impressive number
It reads as a step down from 24.2% and it is not, because every drug in this class loses less weight in people with type 2 diabetes. That is a consistent, well-documented pattern rather than anything specific to retatrutide.
| Drug | Weight loss in type 2 diabetes | Duration |
|---|---|---|
| Retatrutide 12 mg | 15.3% | 40 weeks |
| Tirzepatide 15 mg | ~14.7% | 72 weeks |
| Orforglipron 17.2 mg | 9.6% | 72 weeks |
| Semaglutide 2.4 mg | ~9.6% | 68 weeks |
Retatrutide reached a higher figure in forty weeks than the others reached in sixty-eight to seventy-two, in the population that is hardest for this drug class. These remain separate trials rather than a head-to-head, but they are separate trials in the same population, which is a much closer comparison than the usual cross-trial mixture.
For the same reason, do not read across from 24.2% to what an approved drug does in obesity without diabetes. That comparison is in retatrutide vs Zepbound, with its caveats set out.
The dose-response has not flattened
Look at both trials at the top of the range. In phase 2, 8 mg gave 22.8% and 12 mg gave 24.2% — still climbing. In phase 3, 9 mg gave 13.9% and 12 mg gave 15.3% — still climbing. And in phase 2 the 48-week curve had not levelled off.
Every approved drug in this class flattens: more dose stops buying more weight loss past a point, and more time stops buying it too. Retatrutide has not shown that ceiling in either published trial. Whether it appears in the larger and longer phase 3 obesity studies is one of the open questions the programme exists to answer.
What we still do not know
- The obesity phase 3 results. TRANSCEND-T2D-1 was a diabetes trial. The large obesity studies have not reported.
- What happens past a year. The longest published data is 48 weeks.
- How it compares directly. Head-to-head phase 3 trials against semaglutide (1,250 participants) and tirzepatide (800) are enrolled and running, and neither has reported.
- What happens after stopping. No maintenance or withdrawal data has been published, and weight returns after stopping every drug in this class.
And the constraint that matters most in practice: retatrutide is not approved, so none of these figures are available to anyone outside a trial. What is sold under the name online is covered in the retatrutide overview, including a laboratory analysis of what three vials actually contained.
Against the drugs you can actually get
Three comparisons, each with its caveats set out: vs Zepbound, vs Wegovy and vs Ozempic.
Scientific References
3 sources- 1
Jastreboff AM, Kaplan LM, Frías JP, et al.
Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial
New England Journal of Medicine · 389(6) · 2023PMID: 37366315
NEJM - 2
Bajaj HS, Welch M, Shah P, et al.
Efficacy and safety of retatrutide in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial
The Lancet · 407(10546) · 2026PMID: 42250575
- 3
Jastreboff AM, Aronne LJ, Ahmad NN, et al.
Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1)
New England Journal of Medicine · 387(3) · 2022PMID: 35658024
NEJM
References open in a new tab. Content is reviewed against peer-reviewed literature as part of our editorial policy.
About the author
Editor, Modern Weight Science
Claudiu Gheorghe is the editor of Modern Weight Science. He is not a physician. His role is to synthesize peer-reviewed studies, clinical-trial data, and FDA prescribing information into clear, plain-language explanations, and to make sure every factual claim on the site traces back to a cited source. Any decision about starting, changing, or stopping a medication belongs with a licensed clinician who knows your history.
Every claim is checked against peer-reviewed research through our review process and fact-checking policy.
Frequently Asked Questions
How much weight do you lose on retatrutide?
Two published figures, from two populations. In the phase 2 trial in adults with obesity and without diabetes, mean weight loss was 24.2% at 48 weeks on 12 mg against 2.1% on placebo. In the first phase 3 trial, in adults with type 2 diabetes, it was 15.3% at 40 weeks against 2.6%. The lower number reflects a harder population rather than a weaker result.
Is retatrutide more effective than Zepbound?
The published figures point that way and no head-to-head has reported. The cleanest available comparison is in type 2 diabetes, where retatrutide reached 15.3% in 40 weeks against roughly 14.7% for tirzepatide over 72 weeks — same population, shorter trial, higher figure. Direct phase 3 comparisons against both tirzepatide and semaglutide are enrolled and running.
Did everyone lose weight on retatrutide?
In the phase 2 trial, every participant on 8 mg and 12 mg lost at least 5% of their body weight — 100% of both groups, against 27% on placebo. At the 15% threshold it was 75% and 83% respectively. Those are exceptional response rates for a weight-loss drug, from a trial of 338 people.
Why is the phase 3 weight loss lower than phase 2?
Because it was a different population. Phase 2 enrolled adults with obesity and without diabetes; the phase 3 trial that reported first enrolled adults with type 2 diabetes, where every drug in this class produces less weight loss. It also ran 40 weeks rather than 48. Against other drugs in that same diabetes population, 15.3% is the highest figure published.
How long does retatrutide take to work?
In phase 2, mean weight loss at 24 weeks was 17.5% on the 12 mg dose, rising to 24.2% by 48 weeks — so most of it came in the first half, with the curve still descending at the end of the trial. No data beyond 48 weeks has been published, so where it eventually flattens is unknown.
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Not medical advice. This guide is for general education only. GLP-1 medications, dosing, and treatment suitability are decisions for you and a licensed clinician who knows your full medical history.