Retatrutide's Published Trials, Explained in Plain Language

Short answer: five retatrutide trials have now been published in peer-reviewed journals. The largest, TRIUMPH-1 (New England Journal of Medicine, September 29, 2026), found average weight loss of 25.0% at the 12 mg dose over 80 weeks, against 3.9% on placebo, counting everyone who started the trial. That is lower than the 28.3% Lilly announced in May 2026 because the two numbers answer different questions, explained below. In people with type 2 diabetes (TRIUMPH-2, The Lancet) the 12 mg figure was 18.8% against 5.1%.

This guide summarises each paper in plain language. Our guide to reading clinical trial data covers the general concepts.

Why there are two sets of numbers

Lilly’s press releases lead with the efficacy estimand, which Lilly defines as “efficacy had all randomized participants remained on study intervention.” It estimates what the drug does for people who keep taking it.

The journal papers lead with the treatment-regimen estimand, which is an intention-to-treat analysis: everyone randomised counts, including people who stopped the drug early, whatever happened afterwards. It estimates what happens when the drug is prescribed in real conditions, where some people stop.

Both numbers are valid. The treatment-regimen figure is usually the better guide to what a patient starting the drug can expect; the efficacy figure shows what the drug can do when taken as intended. See the glossary entries for the treatment-regimen estimand and efficacy estimand.

TRIUMPH-1: obesity without diabetes (NEJM, September 2026)

Who: 2,339 adults with obesity and no diabetes, randomised to retatrutide 4 mg, 9 mg or 12 mg once weekly or placebo for 80 weeks. Two subgroups also had knee osteoarthritis (574 people) or obstructive sleep apnea (243 people).

What it measured: three main outcomes, for the 9 mg and 12 mg doses against placebo: weight change, knee pain, and sleep apnea severity.

Dose	Weight change (treatment-regimen)	Weight change (efficacy, Lilly release)
4 mg	-17.6%	-19.0%
9 mg	-23.7%	-25.9%
12 mg	-25.0%	-28.3%
Placebo	-3.9%	-2.2%

The difference from placebo was 19.8 percentage points at 9 mg and 21.0 points at 12 mg, both highly statistically significant.

Knee osteoarthritis: on the WOMAC pain scale (0 to 10, higher is worse), pain fell by 3.5 points at 9 mg and 3.6 points at 12 mg, against 1.9 on placebo. Lilly’s June release described this as a 73.1% reduction; the paper reports it in points, which is the standard clinical measure. More in our osteoarthritis guide.

Sleep apnea: the apnea-hypopnea index fell by 34.3 events per hour at 9 mg and 31.7 at 12 mg, against 9.9 on placebo. These results were published separately in more detail; see Retatrutide for Sleep Apnea.

Side effects: the most common were gastrointestinal. From Lilly’s June 6, 2026 release, at 12 mg versus placebo: nausea 42.4% vs 14.8%, diarrhea 32.0% vs 13.5%, vomiting 25.3% vs 4.8%, constipation 26.1% vs 10.9%, and dysesthesia (unusual skin sensations) 12.5% vs 0.9%. 11.3% stopped the 12 mg dose because of side effects, against 4.9% on placebo.

What it means: TRIUMPH-1 confirms, in a large peer-reviewed trial, that retatrutide produces about a quarter of body weight loss at the top doses over 80 weeks, with the familiar gastrointestinal side effects of the drug class and a higher rate of dysesthesia. Full trial page: TRIUMPH-1.

TRIUMPH-2: obesity with type 2 diabetes (The Lancet, September 2026)

Who: 1,152 adults with type 2 diabetes and a BMI of 27 or more, at 92 sites in 8 countries, randomised to 4 mg, 9 mg, 12 mg or placebo for 80 weeks. Average age 55, average BMI 38.2, average HbA1c 7.7%; 92% were taking oral diabetes medicines. 84% completed treatment.

Dose	Weight change (treatment-regimen, paper)	Weight change (efficacy, Lilly release)
4 mg	-11.9%	-12.7%
9 mg	-16.8%	-19.1%
12 mg	-18.8%	-20.8%
Placebo	-5.1%	-4.0%

Side effects (4 / 9 / 12 mg vs placebo):

	4 mg	9 mg	12 mg	Placebo
Diarrhea	27%	34%	34%	13%
Nausea	14%	21%	28%	8%
Low blood pressure (hypotension)	1%	5%	6%	under 1%
Dysesthesia	4%	6%	7%	1%
Stopped because of an adverse event or death	4%	12%	8%	5%

There were 2, 3 and 1 deaths in the retatrutide groups and 1 on placebo; all were judged unrelated to treatment.

What it means: people with type 2 diabetes lose less weight than people without it, as with every drug in this class, but the 12 mg result is still large, and blood sugar improved substantially. Low blood pressure appeared more often at the higher doses and is worth watching in people already on blood-pressure medicines. More in our type 2 diabetes guide.

The sleep apnea trials (NEJM, October 2026)

A separate NEJM paper reported the sleep apnea groups from both TRIUMPH-1 (243 people) and TRIUMPH-2 (448 people). Apnea-hypopnea index fell by 32 to 34 events per hour at 9 mg and 12 mg in people without diabetes, and about 25 in people with diabetes, against about 10 on placebo. Details in Retatrutide for Sleep Apnea.

TRANSCEND-T2D-1: type 2 diabetes (The Lancet, June 2026)

Who: 537 adults with type 2 diabetes managed by diet and exercise alone (no diabetes medicines), HbA1c 7.0% to 9.5%, at 48 sites in the US, Mexico and India, for 40 weeks. Average HbA1c 7.9%, average BMI 35.8.

Dose	HbA1c change (percentage points)	Weight change
4 mg	-1.69	-11.5%
9 mg	-1.86	-13.9%
12 mg	-1.94	-15.3%
Placebo	-0.81	-2.6%

Between 2% and 5% stopped treatment because of side effects (none on placebo), and there was no severe hypoglycemia. Two deaths, both in the 4 mg group, were judged unrelated. Trial page: TRANSCEND-T2D-1.

Phase 2: where the numbers started (NEJM, 2023)

The Phase 2 obesity trial randomised 338 adults to retatrutide 1, 4, 8 or 12 mg or placebo for 48 weeks. Weight fell by 8.7%, 17.1%, 22.8% and 24.2%, against 2.1% on placebo. At 12 mg every participant lost at least 5% of their weight and 83% lost at least 15%. The Phase 3 trials, which ran longer and in more people, confirmed this signal. See our Phase 2 breakdown.

What is not yet published

TRIUMPH-3 (severe obesity with cardiovascular disease) and TRIUMPH-4 (obesity with knee osteoarthritis) have been reported only in Lilly press releases.
TRANSCEND-T2D-2, which compares retatrutide with semaglutide in type 2 diabetes, completed its main data collection in August 2026; results have not been announced.
TRIUMPH-5, which compares retatrutide with tirzepatide, and the long cardiovascular outcomes trial are still running.

How to read a retatrutide headline

Check which estimand the number uses. Press releases usually lead with the higher efficacy figure; journals with the intention-to-treat figure.
Check the population. Results in people with diabetes are lower than in people without it.
Check the length. Phase 3 obesity trials ran 80 weeks; Phase 2 ran 48.
Compare like with like. Comparisons with other drugs across different trials are approximate; only head-to-head trials such as TRIUMPH-5 can settle them.

Frequently asked questions

How much weight do people lose on retatrutide in the published trials?

In TRIUMPH-1, people without diabetes on 12 mg lost an average of 25.0% of their body weight over 80 weeks when everyone who started is counted, and 28.3% if only people who stayed on treatment are counted. People with type 2 diabetes lost 18.8% and 20.8% on the same two measures.

Why does the NEJM paper say 25% when Lilly said 28%?

They use different analyses. The paper counts everyone who started the trial, including those who stopped the drug; Lilly’s headline figure estimates the effect for people who kept taking it.

Has retatrutide been published in a major journal?

Yes. TRIUMPH-1 and the sleep apnea trials are in the New England Journal of Medicine (2026), TRIUMPH-2 and TRANSCEND-T2D-1 are in The Lancet (2026), and the Phase 2 obesity trial is in the New England Journal of Medicine (2023).

Is retatrutide approved now that it is published?

No. Publication is not approval. Retatrutide is not approved by the FDA or any other regulator. See Is Retatrutide Approved?

This article is for education and is not medical advice. Retatrutide is an investigational drug that is not approved by the FDA or any other regulator.