Retatrutide Clinical Trials

Retatrutide clinical trials have shown substantial weight loss, but the highest percentage in a headline tells only part of the story. Who participated? How long were they followed? What happened to those who stopped treatment?

These details explain why two reports can give different figures for the same study. Here, we examine the results and the questions still being investigated. For an introduction to what retatrutide is and how it works, start with our retatrutide explanation.

What have the published trials found?

Several trials have reported findings from different groups of people. These three Phase 3 studies, larger studies used to evaluate a potential medicine, show why the details matter.

These figures come from analyses that account for people who stop treatment, instead of assuming everyone continues. A placebo contains no active study medicine and provides a comparison group. Sources: TRIUMPH-1, TRIUMPH-2 and TRANSCEND-T2D-1.

The table isn’t a competition between trials. Differences in health conditions, previous treatments and follow-up time can influence the results. Eli Lilly, the company developing retatrutide, funded these studies.

Why do some headlines say 28.3% and others say 25%?

Both figures were reported for the group assigned the highest dose in TRIUMPH-1 at 80 weeks. They answer different questions.

The 28.3% estimate asks what the effect would be if everyone continued the study treatment without starting other weight-management treatments prohibited by the protocol. This is called the efficacy estimand.

The 25.0% estimate considers the assigned treatment whether people continued it or started those other treatments. This is called the treatment-regimen estimand. An “estimand” is the treatment effect an analysis aims to estimate. Retatrutide clinical trials: Lilly’s results and analysis definitions.

These are statistical estimates, not simply two averages calculated by including or excluding everyone who stopped treatment. When comparing reports, check which question each figure answers.

How many people stopped treatment because of side effects?

That figure deserves attention alongside the weight-loss results. In Lilly’s TRIUMPH-1 announcement, treatment discontinuation due to adverse events ranged from 4.1% to 11.3% across the retatrutide groups, compared with 4.9% with placebo. An adverse event is a health problem recorded during a study; the term alone doesn’t establish what caused it. TRIUMPH-1 safety findings.

The published TRIUMPH-2 report identified digestive problems as the most frequent adverse events. Low blood pressure and unusual skin sensations were also reported more often with retatrutide than with placebo. TRIUMPH-2 report.

Stopping the medicine and withdrawing from the study are different things. Someone can stop treatment and still attend follow-up visits. A useful report explains what happened, why, and how missing measurements were handled.

Did the studies measure fat loss or muscle loss?

A smaller study measured body composition, meaning the different tissues that make up body weight. It used scans called DXA, short for dual-energy X-ray absorptiometry, to estimate fat and lean tissue.

Lean tissue includes muscle, organs and water. A decrease in lean tissue on a scan therefore doesn’t mean every pound lost was muscle. How DXA measures lean tissue.

The retatrutide substudy included adults with type 2 diabetes. Of the 189 people enrolled, 103 completed treatment and had both the initial scan and the scan at 36 weeks. The authors reported that the proportion of weight lost as lean mass was similar to that seen with other obesity treatments. This does not show that retatrutide protects muscle or that all the weight lost is fat. Published body-composition study.

What are the comparison and maintenance trials evaluating?

Two studies address questions that weight-loss headlines cannot answer.

TRIUMPH-5 compares retatrutide directly with tirzepatide. Studying both in the same trial offers a more useful comparison than placing percentages from separate studies side by side. Its registry entry has no posted results. TRIUMPH-5.

TRIUMPH-6 investigates how weight loss is maintained. Everyone begins with retatrutide for 80 weeks. During the following 36 weeks, people are assigned to continue the same dose, receive a lower dose or switch to placebo. This design can help examine what happens when treatment changes. Its registry entry also has no posted results. TRIUMPH-6.

The placebo in TRIUMPH-6 is not tirzepatide. These are separate studies with different purposes.

Where can I find participation or follow-up details?

Check the official trial record and the study team’s contact information. When reviewed on October 10, 2026, both TRIUMPH-5 and TRIUMPH-6 were listed as active, not recruiting. They were continuing with people already enrolled and were not accepting new participants.

Older forum posts can describe someone’s experience, but they cannot confirm whether places are available today or whether you qualify. Ask the study team about visits, tests, travel, costs, and the care or follow-up available when participation ends. An extension in one trial doesn’t mean another will offer one.

Retatrutide remains investigational and is not FDA approved. FDA information.

Check who participated, what the comparison group was, and what happened to those who stopped treatment. Those details help you understand the findings behind the headlines about retatrutide clinical trials.