What results does retatrutide show in the trials?

In Eli Lilly's phase 2 obesity trial (Jastreboff et al., NEJM 2023), mean weight reduction reached up to 24.2% over 48 weeks at the highest dose (12 mg) — the highest figure for any incretin agonist in clinical testing at the time. Topline data from the phase 3 TRIUMPH-1 trial (May 2026) reported 28.3% at 80 weeks in 2,339 adults.

How quickly do retatrutide results appear?

The trials use a gradual titration over several weeks, and the weight curve keeps descending across the whole treatment period without clearly plateauing at 48–80 weeks. The largest effect sizes are therefore observed after months of escalating dosing, not in the first weeks.

Are retatrutide's results better than tirzepatide and semaglutide?

In the published pivotal trials the reported figures are 14.9% for semaglutide, 20.9% for tirzepatide and 24.2% for retatrutide in phase 2. These are separate trials with different populations and designs, so they are effect sizes in their own studies rather than a direct head-to-head.

Do these results apply to retatrutide as a research reagent?

No. The efficacy figures come from clinical in vivo research in humans. The retatrutide NorexBio supplies is research-grade peptide intended exclusively for in vitro laboratory use. The clinical results are relevant scientific context but do not apply to use outside a clinical setting.

Trial results

Retatrutide results: 24–28% weight loss in the published trials

What does the research show about retatrutide results? Up to 24.2% weight loss in phase 2 (NEJM 2023) and 28.3% in phase 3 (TRIUMPH-1, 2026). A walk-through of the trial data, timeline and observations — strictly in a research context.

NorexBio Research Team·2 June 2026·7 min read

The question behind “retatrutide results” is simple: how large is the effect in the published research? The answer is that retatrutide has produced the highest effect sizes of any incretin agonist in clinical testing to date, and 2026 phase 3 data reinforced the picture.

Phase 2: up to 24.2% over 48 weeks

The key publication is Jastreboff et al. in the New England Journal of Medicine (2023). The phase 2 obesity trial reported a mean weight reduction of up to 24.2% over 48 weeks at the highest dose (12 mg) — a figure that at the time exceeded anything reported for semaglutide or tirzepatide.

Phase 3 (TRIUMPH-1): 28.3% at 80 weeks

On 21 May 2026, Eli Lilly reported topline results from TRIUMPH-1: a mean weight reduction of 28.3% at 80 weeks in 2,339 adults. The weight curve kept descending across the study period, and tolerability was described as consistent with the GLP-1 class — predominantly mild to moderate gastrointestinal events. We cover the safety picture in detail in the retatrutide side-effects review.

Results in context: 14.9% vs 20.9% vs 24.2%

For reference, the published headline figures are 14.9% for semaglutide and 20.9% for tirzepatide, against retatrutide’s 24.2% in phase 2. These are effect sizes in separate trials with different populations, not a direct head-to-head. We line the molecules up in the retatrutide, tirzepatide and semaglutide comparison.

What the literature actually observes

“Experience” in a research setting means observed outcomes, not anecdotes. The recurring pattern in the published data: the effect is dose-dependent, builds gradually across titration, and the most common observations are gastrointestinal and transient. You can plan the dose-by-dose timeline in our protocol calculator.

Research use, not medical

All of the figures above come from clinical in vivo research. The retatrutide NorexBio supplies is research-grade peptide, pre-filled in pens and intended exclusively for in vitro laboratory use — not for medical, diagnostic or veterinary use. For the product specification, see the Retatrutide product.

Common questions

What researchers ask about this.

What results does retatrutide show in the trials?: In Eli Lilly's phase 2 obesity trial (Jastreboff et al., NEJM 2023), mean weight reduction reached up to 24.2% over 48 weeks at the highest dose (12 mg) — the highest figure for any incretin agonist in clinical testing at the time. Topline data from the phase 3 TRIUMPH-1 trial (May 2026) reported 28.3% at 80 weeks in 2,339 adults.
How quickly do retatrutide results appear?: The trials use a gradual titration over several weeks, and the weight curve keeps descending across the whole treatment period without clearly plateauing at 48–80 weeks. The largest effect sizes are therefore observed after months of escalating dosing, not in the first weeks.
Are retatrutide's results better than tirzepatide and semaglutide?: In the published pivotal trials the reported figures are 14.9% for semaglutide, 20.9% for tirzepatide and 24.2% for retatrutide in phase 2. These are separate trials with different populations and designs, so they are effect sizes in their own studies rather than a direct head-to-head.
Do these results apply to retatrutide as a research reagent?: No. The efficacy figures come from clinical in vivo research in humans. The retatrutide NorexBio supplies is research-grade peptide intended exclusively for in vitro laboratory use. The clinical results are relevant scientific context but do not apply to use outside a clinical setting.

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