TRIUMPH-1 Phase 3 Topline Results: Retatrutide Achieves 28.3% Weight Loss at 80 Weeks

Eli Lilly's TRIUMPH-1 reported May 21, 2026: 2,339 participants, 80-week duration, 28.3% mean weight loss at 12 mg. The largest Phase 3 obesity trial efficacy signal ever recorded. Full data breakdown with cross-trial comparison.

On May 21, 2026, Eli Lilly released topline results from TRIUMPH-1 (NCT05929066), the pivotal Phase 3 clinical trial of retatrutide in adults with obesity or overweight — the trial that will anchor the weight-management NDA. The results represent the largest weight-loss signal ever reported in a Phase 3 randomized controlled trial of an anti-obesity medication.

Trial Design

TRIUMPH-1 was a randomized, double-blind, placebo-controlled, 80-week master trial enrolling 2,339 participants with BMI ≥30 (or ≥27 with at least one weight-related comorbidity) without type 2 diabetes. Three retatrutide doses (4 mg, 9 mg, 12 mg) were evaluated against placebo.

The trial duration — 80 weeks — is the longest in the TRIUMPH program and was designed as a direct analogue to SURMOUNT-1 (tirzepatide, 72 weeks) and STEP-1 (semaglutide, 68 weeks), establishing cross-trial comparability for the eventual NDA package.

A prespecified blinded extension included 532 participants with baseline BMI ≥35 who completed the main trial and tolerated the study medication.

Primary Efficacy Results

All three doses met primary and key secondary endpoints:

At the 12 mg dose, 65.3% of participants achieved BMI below 30 kg/m² (the obesity threshold), representing a clinically significant categorical shift.

Cardiometabolic Outcomes

TRIUMPH-1 reported significant improvements across cardiometabolic risk markers, consistent with TRIUMPH-4 signals:

• Waist circumference: 24.1 cm average reduction (12 mg dose, extrapolated from TRIUMPH-4; TRIUMPH-1 detailed data pending ADA presentation)
• Non-HDL cholesterol, triglycerides, systolic blood pressure, hsCRP: Favorable shifts across all doses (magnitude pending full publication)
• LDL cholesterol: Approximately 20% reduction reported in TRIUMPH-4; TRIUMPH-1 subgroup data expected June 2026

Cross-Trial Comparison: Retatrutide vs. Tirzepatide vs. Semaglutide

These are indirect cross-trial comparisons. No head-to-head Phase 3 data exists. TRIUMPH-5 is the first active-comparator trial and has not yet reported.

The incremental gain at each receptor expansion is approximately 5–6 percentage points. The glucagon component appears to contribute meaningful additional efficacy through increased energy expenditure and hepatic lipid clearance — mechanisms not present in mono- or dual-agonist compounds.

Safety Signal Summary

Detailed safety data from TRIUMPH-1 is pending the full ADA presentation. Based on the available topline release and prior TRIUMPH-4 data:

• GI adverse events (nausea, diarrhea, vomiting) were the most common, consistent with the GLP-1 class
• TRIUMPH-4 reported an 18% discontinuation rate at 12 mg — approximately 2.5× higher than typical semaglutide/tirzepatide trial discontinuation rates (~7%)
• Dysesthesia (abnormal skin sensation) is a retatrutide-specific signal not seen with semaglutide or tirzepatide, reported primarily during dose escalation
• Full TRIUMPH-1 safety data, including discontinuation rates by dose, will be critical for the NDA risk-benefit assessment

Regulatory Timeline

TRIUMPH-1 was the final pivotal trial needed for the weight-management NDA package. Seven additional Phase 3 TRIUMPH readouts are expected in 2026:

• TRIUMPH-2: Adults with obesity/overweight + type 2 diabetes — expected Q2–Q3 2026
• TRIUMPH-3: Adults with obesity/overweight + established cardiovascular disease — expected H2 2026
• TRIUMPH-5: Active-comparator trial (head-to-head vs. another agent) — timeline TBD
• Additional trials in sleep apnea, chronic low back pain, MASLD, and renal outcomes

Regulatory submission is anticipated in late 2026 or early 2027. FDA approval, if granted, would likely come in 2027–2028.