TRIUMPH-4 Phase 3 Results:
28.7% Weight Reduction

Trial Overview

TRIUMPH-4 is one of several Phase 3 trials in Eli Lilly's TRIUMPH program evaluating Retatrutide for obesity and weight-related comorbidities. The trial enrolled adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related condition. Participants received once-weekly subcutaneous injections of Retatrutide at escalating doses up to 12mg, or placebo, over a 48-week treatment period.

Primary Endpoint Results

The 12mg dose group achieved a mean body weight reduction of 28.7% from baseline — the highest figure ever reported for a single compound in a Phase 3 obesity trial. For context, the GLP-1 agonist semaglutide achieved approximately 15% in the STEP trials, and the dual GIP/GLP-1 agonist tirzepatide achieved approximately 21% in SURMOUNT-1.

The 28.7% figure represents a nearly two-fold improvement over semaglutide and a 37% relative improvement over tirzepatide. This magnitude of weight loss approaches what was previously achievable only through bariatric surgery.

Secondary Endpoints

Osteoarthritis Pain

A pre-specified secondary analysis evaluated knee pain in participants with obesity-related osteoarthritis. The Retatrutide group showed a 75.8% reduction in knee pain scores compared to baseline, a finding attributed to both mechanical offloading from weight loss and potential direct anti-inflammatory effects of GLP-1 receptor activation in joint tissue.

Hepatic Steatosis

Consistent with Phase 2 data, TRIUMPH-4 confirmed significant liver fat reduction. Over 90% of participants with baseline MASLD (metabolic dysfunction-associated steatotic liver disease) achieved normalization of liver fat to below 5%, as measured by MRI-PDFF. This effect is driven primarily by Glucagon receptor-mediated hepatic lipolysis — a mechanism unique to Retatrutide among incretin-based therapies.

Safety Profile

The most common adverse events were gastrointestinal: nausea, diarrhea, and decreased appetite, consistent with the GLP-1 class effect. These were predominantly mild to moderate in severity and tended to decrease after the dose-escalation period. Discontinuation rates due to adverse events were comparable to those observed in tirzepatide trials.

Significance for Research

TRIUMPH-4 establishes Retatrutide as the most potent single-compound intervention for weight reduction in clinical development. For researchers studying incretin-based metabolic pathways, the data confirms that adding Glucagon receptor activation to the GIP/GLP-1 backbone produces a non-additive, synergistic enhancement of metabolic outcomes. The Glucagon component is not merely additive — it opens a thermogenic pathway that fundamentally changes the energy balance equation.