TRIUMPH-1: retatrutide for weight loss over 80 weeks

Why this study matters

Retatrutide is an experimental medicine. As of October 2026, it is not approved in Canada or in any other country, and this study is research only. Retatrutide acts on three hormone receptors at once: GIP, GLP-1 and glucagon. TRIUMPH-1 is a phase 3 trial, the large, late-stage kind of study that regulators usually rely on. It followed an earlier phase 2 dose-finding trial. Besides weight, it also looked at knee pain and sleep apnea in two smaller groups of people within the trial.

Who was in the study

The trial randomized 2339 adults living with obesity. None had diabetes. Within the trial, 574 people had knee osteoarthritis, a joint condition that causes pain and stiffness. Another 243 people had obstructive sleep apnea, a condition where breathing stops or becomes shallow many times during sleep. The trial ran for 80 weeks. The published summary we reviewed does not report the age range, starting weight, BMI or the countries where the trial ran.

What the researchers did

This was a phase 3, randomized, double-blind trial. Randomized means people were assigned to a group by chance. Double-blind means neither participants nor study staff knew who was getting the medicine and who was getting placebo, an inactive injection that looks the same.

People received a weekly injection under the skin of retatrutide at 4 mg, 9 mg or 12 mg, or placebo, for 80 weeks. The published summary we reviewed does not say whether people also received diet or activity support.

The trial had three main questions, each comparing the 9 mg and 12 mg groups with placebo:

• the percentage change in body weight
• in people with knee osteoarthritis, the change in a knee pain score called WOMAC (the summary describes it as ranging from 1 to 10, with higher scores meaning worse pain)
• in people with sleep apnea, the change in the apnea-hypopnea index, which counts how many times per hour breathing stops or becomes shallow during sleep

An estimand is the exact question the statistics answer. For weight, the researchers used a treatment-regimen estimand, also called intention-to-treat. It counts everyone who was randomized, whether or not they kept taking the medicine. For knee pain and sleep apnea, the main analysis used a "hybrid" estimand, which handles people who stopped treatment differently. The researchers also reported intention-to-treat results for those groups.

What they found

At 80 weeks, average weight change was -17.6% with 4 mg, -23.7% with 9 mg and -25.0% with 12 mg, compared with -3.9% with placebo. The differences from placebo were -19.8 percentage points for 9 mg and -21.0 for 12 mg, each with P below 0.001 (R33-C01). A P value this small means a difference this large would be very unlikely if the medicine had no effect. The published summary we reviewed does not give confidence intervals for these results.

In people with knee osteoarthritis, pain scores fell in all groups, and fell more with retatrutide (R33-C02).

The differences from placebo were -1.6 and -1.8 points (9 mg and 12 mg) with the hybrid estimand, and -1.4 and -1.6 points with intention-to-treat. All had P below 0.001.

In people with sleep apnea, counting everyone randomized, breathing events changed by -22.8, -34.3 and -32.1 events per hour with 4, 9 and 12 mg, compared with -9.6 with placebo. The differences from placebo were -24.7 (9 mg) and -22.5 (12 mg), both with P below 0.001 (R33-C03). With the hybrid estimand, the differences were -24.4 and -21.9. We do not show the hybrid result for each group, because one of those values appears to be printed without its minus sign in the abstract and we could not check it against the full paper.

Side effects and people who stopped

The abstract says the most common side effects were gastrointestinal, meaning stomach and bowel symptoms. The published summary we reviewed does not report how often each side effect happened, how many people stopped treatment, how many stopped because of side effects, or the number of serious side effects in any group.

What this study does not tell you

• The trial did not include people with diabetes (TRIUMPH-2 studied type 2 diabetes). It ran for 80 weeks, so it does not show longer-term results or what happens after stopping.
• Our summary is based on the abstract only. It does not give confidence intervals, side effect rates or how many people stopped treatment.
• The knee pain and sleep apnea results come from smaller groups within the trial, not from the whole trial.
• Company news releases and media stories may report a different estimand, such as results only in people who kept taking the medicine. Those numbers are not the same as the intention-to-treat results shown here.
• Do not compare these percentages with trials of other medicines, which enrolled different people and used different methods.
• The trial was funded by Eli Lilly, the company developing retatrutide, and several authors work for the company.

What it means in Canada

As of October 2026, retatrutide is not approved in Canada or in any other country. On 9 April 2026, Health Canada issued a warning about unauthorized peptides sold online, and retatrutide was among them. This trial does not change that status. You can follow emerging medicines on our medicines page. For medicines available in Canada, see semaglutide in Canada, tirzepatide in Canada and public drug coverage by province.

Related reading

Other studies in this library that bear on the same question.

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