Retatrutide clinical trials and weight-loss results

Retatrutide weight-loss studies, the Phase 3 TRIUMPH programme, safety findings and the direct comparison with tirzepatide, the active ingredient in Mounjaro.

By Manchester Peptides · Published 5 November 2026

On this page

What is retatrutide and why is it being studied?

Retatrutide (LY3437943) is an investigational molecule that activates the GIP, GLP-1 and glucagon receptors. Tirzepatide, the active ingredient in Mounjaro, activates GIP and GLP-1. Eloralintide targets an amylin receptor. These differences explain why researchers study them separately. A receptor count by itself cannot predict weight loss, tolerability or long-term clinical outcomes.

Lilly reports that retatrutide remains investigational. The Phase 3 programme covers several populations, including people with obesity without diabetes, people with type 2 diabetes, and people with other weight-related conditions. The published TRIUMPH programme design sets out which questions the studies were designed to answer.

How the retatrutide research programme developed

2023: published Phase 2 trials examined retatrutide in adults with obesity and, separately, in adults with type 2 diabetes. The diabetes study included dulaglutide as an active comparator.
2024: a substudy investigated liver fat in a selected group from the earlier obesity trial. The outcome was liver fat rather than total weight.
2026: published Phase 3 research covered obesity and diabetes, while sponsor updates and registry entries described additional populations and planned outcomes.

TRIUMPH asks several obesity-related questions. TRANSCEND-T2D investigates type 2 diabetes. A shared drug name does not make the starting populations, outcomes or control groups interchangeable. Phase 2 diabetes trial · TRIUMPH trial designs.

Retatrutide weight loss in Phase 2 and Phase 3

Retatrutide results by population, follow-up and source
Study	Who or what it studied	What it reported
Phase 2 obesity trial	338 adults, placebo-controlled. Primary weight-change endpoint at 24 weeks with follow-up to week 48.	In the highest studied group, mean weight loss reached 24.2% at week 48, versus 2.1% with placebo. Peer-reviewed trial
TRIUMPH-1	Phase 3 in adults with obesity without diabetes, 80 weeks.	The journal's treatment-regimen analysis reported 17.6%, 23.7% and 25.0% mean weight loss, versus 3.9% with placebo. Lilly's separate efficacy estimate was 19.0%, 25.9% and 28.3%, versus 2.2%. Peer-reviewed paper · Sponsor figures and analysis
TRIUMPH-2	Phase 3 in adults with overweight or obesity and type 2 diabetes, 80 weeks.	Lilly reported up to 20.8% mean weight loss versus 4.0% with placebo using its efficacy estimate. Peer-reviewed paper · Sponsor figures
TRIUMPH-3	Phase 3 in adults with class II or III obesity and cardiovascular disease, 80 weeks.	Lilly reported up to 22.6% mean weight loss versus 3.2% with placebo using its efficacy estimate. This is a body-weight result in the enrolled population. Sponsor programme summary
TRIUMPH-4	Phase 3 in adults with obesity or overweight and knee osteoarthritis, 68-week outcomes.	Lilly reported up to 28.7% mean weight loss versus 2.1% with placebo. The trial separately assessed knee pain. Study registry · Sponsor figures

The Phase 3 rows above identify sponsor efficacy estimates where those figures come from Lilly. An efficacy estimate describes what the analysis expects under continued treatment conditions. A treatment-regimen estimate can produce different numbers because it answers a question that also accounts for outcomes such as discontinuation. Check the estimate, comparison group and time point before comparing weight-loss results.

What else has the TRIUMPH programme measured?

The retatrutide programme measures different outcomes in different groups. TRIUMPH-4 measured knee pain in people with knee osteoarthritis. The published TRIUMPH-1-OSA and TRIUMPH-2-OSA trials examined breathing disruptions during sleep in people with obstructive sleep apnoea, with and without type 2 diabetes. Those sleep and knee outcomes are separate from the primary weight-loss figures. A finding in a trial does not establish a licensed indication. Read the sleep apnoea trials.

Lilly also reported a 104-week TRIUMPH-1 extension in a group that had a baseline BMI of at least 35. The extension group was narrower than the main study population. Its results should be read separately from the main 80-week result.

Retatrutide in type 2 diabetes, liver fat and body-composition studies

Published retatrutide studies that measure more than body weight
Study	Who or what it studied	What it reported
Phase 2 type 2 diabetes trial	Randomised study with placebo and an active dulaglutide comparison.	The study examined HbA1c and body weight in adults with type 2 diabetes. The active comparison concerns dulaglutide, a different medicine from Mounjaro. Read the published trial
TRANSCEND-T2D-1	Phase 3 in adults with type 2 diabetes with inadequate glucose control on diet and exercise alone. Primary time point at 40 weeks.	In Lilly's efficacy analysis, HbA1c fell by 1.7 to 2.0 percentage points across retatrutide groups, versus 0.8 with placebo. Mean weight loss reached 16.8% in one group, versus 2.5% with placebo. Peer-reviewed trial · Sponsor efficacy estimates
Phase 2a liver-fat substudy	98 participants from the obesity study with metabolic dysfunction-associated steatotic liver disease and at least 10% liver fat at baseline.	In the highest studied group, liver fat fell by 82.4% relative to its starting value at week 24, compared with a 0.3% increase with placebo. That percentage refers to liver fat. Read the substudy
Phase 2 body-composition substudy	A subset of the type 2 diabetes trial underwent body-composition assessment.	The analysis looked at fat and lean mass alongside total weight. It provides more detail than the scale alone. It does not establish whether changes in body composition translated into changes in strength. Read the substudy

Changes in HbA1c, liver fat or body weight each tell a different story. A reduction in liver fat on a scan does not establish that fibrosis resolved or that future liver complications were prevented. Those outcomes require other measurements and longer follow-up.

Which retatrutide trials are still answering open questions?

Registered retatrutide studies and their planned outcomes
Study	Who or what it studied	What it reported
TRIUMPH-5	Randomised comparison with tirzepatide, the active ingredient in Mounjaro.	The primary endpoint is percent change in body weight at week 80. Waist circumference, blood pressure and other measures are secondary outcomes. NCT06662383
TRIUMPH-6	Weight maintenance study. After an 80-week lead-in on retatrutide, participants are assigned to continue under one of two regimens or switch to placebo for 36 weeks.	Designed to compare weight maintenance and changes after withdrawal in people who reached randomisation. NCT06859268
TRIUMPH-8	Phase 3 placebo-controlled trial in adults with obesity or overweight.	Evaluates body-weight reduction and safety in the enrolled population. NCT07232719
TRIUMPH-Outcomes	Adults with BMI at least 27 and atherosclerotic cardiovascular disease, chronic kidney disease, or both.	Designed to measure serious cardiovascular events and progression of kidney disease. NCT06383390

Read these as registered questions. Whether a trial is recruiting, has finished recruiting or is complete does not tell you what it found. The registry's results tab and subsequent peer-reviewed reports are where those answers can appear.

Retatrutide safety and unanswered questions

Gastrointestinal adverse effects were frequent in the Phase 2 trial. The investigators also reported dose-related increases in heart rate, which peaked during follow-up and later declined. Phase 3 reports add more safety information, but longer follow-up and regulatory assessment remain important for understanding uncommon harms, outcomes after stopping and safety across different patient groups.

A laboratory report for a named sample can answer analytical questions about that sample. Retatrutide clinical trial results refer to the study formulation and protocol. Weight loss in a study cannot establish that material outside the study is equivalent, safe or effective.

How to read retatrutide safety tables

Check the number of people studied in each group and how long they were followed. Keep any adverse event, a serious event and discontinuation because of an event as separate categories. A study can find substantial weight loss while some participants stop because of side effects. When reviewing the full paper, compare adverse events and discontinuations against the control group and read the authors' definitions.

Retatrutide vs Mounjaro: the trial that compares them

TRIUMPH-5 is a randomised Phase 3 trial of retatrutide versus tirzepatide, the active ingredient in Mounjaro, in adults with obesity. The sponsor lists recruitment as complete. No head-to-head results were located when this guide was updated. Registration describes the comparison the researchers intend to make. Read the TRIUMPH-5 record or the three-way research comparison.