TRIUMPH-1, the pivotal retatrutide trial, was published in the New England Journal of Medicine on 29 September 2026, four months after Lilly announced the headline figures.1
The numbers held: 28.3% weight loss at 12 mg over 80 weeks in 2,339 adults, against 2.2% on placebo. Two thirds of the top-dose group finished the trial no longer meeting the criteria for obesity.
Two things deserve more attention than the headline. Abnormal skin sensation occurred in 12.5% of the top-dose group against 0.9% on placebo, roughly fourteen times the placebo rate. And in a trial where people lost an average of 70 pounds, nobody measured how much of that was fat and how much was muscle.
What the trial found
The full dose range, counted both ways.
| At 80 weeks | Stayed on treatment | Everyone randomised |
|---|---|---|
| Retatrutide 4 mg | -19.0% | -17.6% |
| Retatrutide 9 mg | -25.9% | -23.7% |
| Retatrutide 12 mg | -28.3% | -25.0% |
| Placebo | -2.2% | -3.9% |
Among those on 12 mg, 62.5% lost at least a quarter of their body weight and 45.3% lost at least 30%. Two thirds, 65.3%, finished with a BMI under 30, and a third were under 25.
Cardiometabolic markers moved with the weight: triglycerides down 41.0%, non-HDL cholesterol down 24.2%, systolic blood pressure down 12.3 mmHg, waist circumference down 24.1 cm.2
The paper also notes something unusual: no weight-loss plateau through the full 80 weeks. The curve was still descending when the trial ended.
Why do sites report different numbers for this trial?
Because there are two legitimate ways of counting, and the placebo row shows what the difference measures.
The first column is the efficacy estimand: what happened among people who stayed on the drug. The second is the treatment-regimen estimand: what happened to everyone who was randomised, including those who stopped early.
Look at the placebo row. On the first measure placebo lost 2.2%; on the second it lost 3.9%. The placebo group did better when you count everyone, because people who left the placebo arm were not the ones doing well on it.
Neither number is the honest one and the other a spin. They answer different questions. If you want to know what the drug does when taken as directed, read the first. If you want to know what happens to a group of people prescribed it, read the second. Headlines quote the first; a prescriber thinks in terms of the second.
Does the trial report muscle loss?
No, and it was never going to. TRIUMPH-1 has no body composition substudy.
The programme's published design paper sets out the endpoints for all four trials, and it is explicit: TRIUMPH-3 includes a substudy measuring body composition by DXA in approximately 100 participants, to assess change in total body fat and lean mass.3 TRIUMPH-1 has none. Across a programme of more than 5,800 people, body composition is being measured in about a hundred of them, and that hundred sits in the cardiovascular trial, which has not published.
So the pivotal obesity trial, 2,339 people, 80 weeks, 70 pounds of average weight loss at the top dose, reports waist circumference and nothing else about what the body lost.
The comparison is the part that matters. SURMOUNT-1, the pivotal tirzepatide trial, ran a DXA substudy of 255 participants and reported that roughly 75% of the weight lost was fat and 25% lean. The semaglutide programme ran equivalent substudies. Those numbers exist because somebody planned to collect them.
Estimates of how much of the loss is lean tissue vary by trial and by method, from about a quarter in the tirzepatide substudy to higher figures elsewhere, which our guide on weight loss sets out. For the compound producing the largest losses ever recorded, there is no figure at all, and the data that will eventually give one comes from about 100 people with cardiovascular disease rather than from the 2,339 in the trial everyone is quoting.
None of that means anything was hidden. Body composition substudies are expensive, need DXA scanners at participating sites, and are routinely run in one trial of a programme rather than all four. But a reader asking how much of 70 pounds was muscle is asking a reasonable question, and the answer today is that nobody has published it.
Skin sensation, now at scale
The phase 2 trial reported cutaneous hyperesthesia in 7% of participants against 1% on placebo, in 338 people. It read as a curiosity.
TRIUMPH-1 reports dysesthesia in 5.1%, 12.3% and 12.5% of the 4, 9 and 12 mg groups, against 0.9% on placebo.1 The knee osteoarthritis trial reported 20.9% at 12 mg against 0.7%.
So the signal held at eight times the sample size, it tracks dose, and at the top dose it runs roughly fourteen times the placebo rate. The events are described as generally mild and most participants continued treatment.
This is the effect people describe on forums as sandpaper skin, burning, or sensitivity to a shirt seam. It is not a rare curiosity and it is not in anyone's imagination. Our guide on it covers what the trials found and what to say to a clinician.
What else the publication shows
Gut effects dominated and rose with dose: nausea 42.4%, diarrhoea 32.0%, vomiting 25.3% and constipation 26.1% at 12 mg.
Discontinuation because of adverse events ran 4.1%, 6.9% and 11.3% across the three doses, against 4.9% on placebo. The top dose is the one people leave.
In the sleep apnoea subgroup, retatrutide reduced the apnoea-hypopnoea index by roughly 23 to 34 events an hour against about 10 on placebo.2
Who was in the trial?
2,339 adults. Four things about them shape every figure above.
TRIUMPH-1 enrolled 2,339 adults with obesity, or overweight with at least one weight-related condition, and specifically without type 2 diabetes. That exclusion matters: weight loss on these drugs is consistently smaller in people with diabetes, which is why TRIUMPH-2 in a diabetic population produced 20.8% at the same dose rather than 28.3%.
The trial ran 80 weeks, longer than the 68 and 72 weeks used in the pivotal trials of semaglutide (Wegovy) and tirzepatide (Zepbound), and it included a subgroup with obstructive sleep apnoea.
So the headline figure describes a non-diabetic population, on the highest dose, over a longer period, among people who stayed on treatment. Each of those four conditions makes the number larger than it would be elsewhere, and none of them makes it wrong.
What is the 30.3% figure?
That comes from the two-year extension. It is the largest number anyone has reported for a weight-loss drug.
A subset of participants with a BMI of 35 or higher, who completed the main trial and tolerated their dose, continued to 104 weeks. In that group the average loss reached 30.3%.1
Two caveats travel with that figure and are usually dropped. It is a selected subset: people who had already tolerated two years of treatment, not everyone who started. And a higher starting BMI means more weight available to lose, which flatters a percentage.
It is still the largest average weight loss published for a drug, and it is the figure that invites the comparison with bariatric surgery that Lilly's own announcement made.
What is still to come
Three things are outstanding. The first is the one to watch.
TRIUMPH-6 is testing maintenance: 80 weeks on the drug, then a randomised phase where people either continue, drop to a lower dose, or switch to placebo. That answers the question this class has barely addressed, which is what happens when you stop or step down, and it is the same design that produced the tirzepatide maintenance result earlier this year.
TRIUMPH-3 and TRIUMPH-4 are still topline announcements rather than published papers. Until they publish, their figures carry less weight than TRIUMPH-1's, including the 20.9% dysesthesia rate from the knee trial.
And the filing: Lilly restated on 29 September that it intends to submit in the first quarter of 2027. There is also an unresolved question about whether retatrutide is regulated as a biologic, which would change the type of application filed.
What this does not change
Retatrutide is still approved nowhere. Lilly restated on 29 September that it plans to file with the FDA in the first quarter of 2027,2 which puts a prescription realistically in 2028.
And none of this describes the vial on a research site. TRIUMPH-1 tested a pharmaceutical product, manufactured by Lilly, given at known doses under supervision, to people who were monitored. The compound sold online shares a name with it. Our coverage of the counterfeit vial that put a patient in hospital is the other half of that picture.
Common questions
Has the retatrutide phase 3 trial been published?
Yes. TRIUMPH-1 was published in the New England Journal of Medicine on 29 September 2026. TRIUMPH-2 was published in The Lancet the same week. TRIUMPH-3 and TRIUMPH-4 remain topline announcements.
How much weight did people lose in TRIUMPH-1?
At 12 mg over 80 weeks, 28.3% among those who stayed on treatment, or 25.0% counting everyone randomised, against 2.2% and 3.9% on placebo. At 4 mg and 9 mg it was 19.0% and 25.9%.
Why do different sites give different numbers for this trial?
Because there are two legitimate ways of counting. One measures what happened among people who stayed on the drug, the other includes everyone who was randomised. Both appear in the paper.
Does the trial say how much muscle people lost?
No, and it was not designed to. The TRIUMPH programme's design paper places its only body composition substudy in TRIUMPH-3, the cardiovascular trial, in about 100 participants. TRIUMPH-1 measured waist circumference and nothing else about body composition.
Why does the tirzepatide trial have that number and this one does not?
Because SURMOUNT-1 ran a DXA substudy of 255 participants and TRIUMPH-1 ran none. That substudy is where the roughly 75% fat to 25% lean figure for tirzepatide comes from.
How common was the skin sensation effect?
Dysesthesia occurred in 5.1%, 12.3% and 12.5% at 4, 9 and 12 mg against 0.9% on placebo. The knee osteoarthritis trial reported 20.9% at 12 mg. Events were generally mild and most participants continued treatment.
How many people stopped because of side effects?
Between 4.1% and 11.3%, rising with the dose, against 4.9% in the placebo group. The top dose is where people leave.
What was the 30.3% figure?
A subset of participants with a BMI of 35 or higher, who completed the main trial and tolerated their dose, continued to 104 weeks and averaged 30.3%. It is a selected group rather than everyone who started, and a higher starting BMI means more weight available to lose.
Why did people with diabetes lose less?
They were not in this trial. TRIUMPH-1 excluded type 2 diabetes. The separate diabetes trial, TRIUMPH-2, produced 20.8% at the same dose, which is the consistent pattern across this drug class.
Does publication mean retatrutide is close to approval?
It is a step, not the step. Lilly plans to file in the first quarter of 2027, and a filing is not a decision. A prescription is realistically 2028.
Does any of this apply to retatrutide bought online?
Not directly. The trial tested a Lilly-manufactured product at known doses with monitoring. A vial from a research site shares the name and nothing else that can be verified.
Sources
- Jastreboff AM, Kaplan LM, Davies MJ, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. *New England Journal of Medicine*, published online 29 September 2026. [doi:10.1056/NEJMoa2604169](https://www.nejm.org/doi/full/10.1056/NEJMoa2604169). NCT05929066. *Phase 3 trial, 2,339 adults with obesity or overweight and at least one weight-related condition, without diabetes, randomised to retatrutide 4, 9 or 12 mg or placebo for 80 weeks. Weight change on the efficacy estimand: -19.0%, -25.9%, -28.3% against -2.2%; on the treatment-regimen estimand: -17.6%, -23.7%, -25.0% against -3.9%. At 12 mg, 62.5% lost at least 25% and 45.3% at least 30%; 65.3% reached a BMI below 30 and 33.3% below 25. Dysesthesia 5.1%, 12.3% and 12.5% against 0.9%. Discontinuation for adverse events 4.1%, 6.9% and 11.3% against 4.9%. Nausea 42.4%, diarrhoea 32.0%, vomiting 25.3% and constipation 26.1% at 12 mg. Triglycerides -41.0%, non-HDL cholesterol -24.2%, systolic blood pressure -12.3 mmHg, waist circumference -24.1 cm. The paper reports waist circumference and no other measure of body composition; the programme's design paper confirms TRIUMPH-1 had no DXA substudy. Figures cross-checked against Lilly's accompanying release and independent trade reporting, which agree.* ↩
- Eli Lilly and Company. Results announcement accompanying the publication of TRIUMPH-1 and TRANSCEND-T2D-1, 29 September 2026. *Company release. Source for the cardiometabolic figures quoted here (triglycerides -41.0%, non-HDL cholesterol -24.2%, systolic blood pressure -12.3 mmHg, waist circumference -24.1 cm at 80 weeks), the sleep apnoea subgroup results, the proportions reaching a BMI below 30 and below 25, and the restated intention to file with the FDA in the first quarter of 2027. The release states that its data are based on the efficacy estimand.* ↩
- Giblin K, et al. Retatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: Rationale and design of the TRIUMPH registrational clinical trials. *Diabetes, Obesity and Metabolism*, 2026. [doi:10.1111/dom.70209](https://doi.org/10.1111/dom.70209). *Open access design paper covering all four registrational trials, with a table of objectives, endpoints and designs for each. States that TRIUMPH-3 includes a substudy to measure body composition via DXA in approximately 100 participants, to assess percent and absolute change in total body fat and lean mass. No equivalent substudy is listed for TRIUMPH-1, TRIUMPH-2 or TRIUMPH-4. Programme total is more than 5,800 participants.* ↩
Citing this page. Peptide Decoding. The Retatrutide Trial Is Published. It Never Measured Muscle. Figures from the published trial and Lilly's accompanying release. https://peptidedecoding.com/news/triumph-1-published