TRIUMPH-1 Phase 3 Results: Retatrutide Weight Loss at 80 Weeks

TRIUMPH-1 is a Phase 3 clinical trial evaluating once-weekly retatrutide in adults with obesity or overweight without diabetes. Eli Lilly reported topline results showing mean body-weight reductions of 19.0% (4 mg), 25.9% (9 mg), and 28.3% (12 mg) at 80 weeks. Lilly reported 2,339 randomized participants; ClinicalTrials.gov lists actual enrollment of 2,335. These are topline results; peer-reviewed publication is pending. Retatrutide remains investigational and is not FDA approved.

May 2026

Eli Lilly and Company; ClinicalTrials.gov NCT05929066

View Source

Introduction

TRIUMPH-1 is a Phase 3 clinical trial evaluating once-weekly retatrutide in adults with obesity or overweight without diabetes. Eli Lilly reported topline results showing substantial mean body-weight reductions after 80 weeks of treatment.

Retatrutide remains investigational and is not FDA approved.

Study Design

TRIUMPH-1 randomized participants to once-weekly retatrutide 4 mg, 9 mg, 12 mg, or placebo.

Lilly reported 2,339 randomized participants. ClinicalTrials.gov lists actual enrollment of 2,335 participants.

The primary weight-management endpoint was evaluated at Week 80.

Weight-Loss Results

According to Eli Lilly's reported Phase 3 topline results, mean body-weight reductions at Week 80 were:

19.0% with retatrutide 4 mg
25.9% with retatrutide 9 mg
28.3% with retatrutide 12 mg

These figures should not be confused with results from the earlier Phase 2 obesity study.

Phase 2 vs. Phase 3

The earlier Phase 2 obesity trial evaluated retatrutide over 48 weeks and reported mean body-weight reduction of up to 24.2% in the highest-dose group.

That 24.2% figure belongs to the Phase 2 study.

The 28.3% result at 80 weeks belongs to the Phase 3 TRIUMPH-1 study.

The studies differ in design, population, duration, and stage of clinical development and should not be presented as the same trial.

104-Week Extension

Lilly subsequently reported results from an extension involving TRIUMPH-1 participants with baseline BMI of at least 35 kg/m².

In that population, the 12 mg group achieved mean body-weight reduction of up to 30.3% at 104 weeks.

The extension result represents a defined study population and should not be generalized to every patient.

Interpreting the Results

TRIUMPH-1 provides Phase 3 evidence regarding retatrutide for chronic weight management.

However, topline company-reported findings and peer-reviewed publications should be clearly distinguished.

Individual outcomes can differ substantially from study averages.

Retatrutide remains investigational. There is currently no FDA-approved retatrutide prescribing information.

Sources

Primary sources: