What Happened
On December 11, 2025, Eli Lilly announced topline results from TRIUMPH-4, a Phase 3, double-blind, placebo-controlled trial of retatrutide -- an investigational once-weekly injectable that activates GIP, GLP-1, and glucagon receptors -- in 445 adults with obesity or overweight and knee osteoarthritis. Participants were randomized 1:1:1 to retatrutide 9 mg, retatrutide 12 mg, or placebo for 68 weeks. Lilly reported that the trial met its primary endpoint.
Why It Matters
TRIUMPH-4 is one of eight pivotal Phase 3 trials in Lilly's TRIUMPH program for retatrutide. This readout is notable both for the reported magnitude of weight loss and because it is the first retatrutide Phase 3 trial to report a musculoskeletal/pain outcome (knee osteoarthritis symptoms) alongside weight loss, rather than a purely metabolic or weight endpoint.
What the Evidence Showed
Lilly reported average body-weight loss of 28.7% (approximately 71.2 lbs) at 68 weeks in the 12 mg retatrutide group, versus 26.4% in the 9 mg group and 2.1% in the placebo group. The company also reported a mean reduction in WOMAC pain score of 4.5 points (75.8%) in the retatrutide groups, with more than one in eight retatrutide-treated participants reporting complete resolution of knee pain by the end of the trial.
What This Does Not Establish
These are sponsor-reported topline results, not yet peer-reviewed or published in full. Lilly has stated that detailed TRIUMPH-4 results will be presented at a future medical meeting and published in a peer-reviewed journal; the full statistical analysis, safety data, and methods have not yet been independently reviewed. Retatrutide is investigational and is not FDA-approved for any indication -- this trial result does not establish approval, availability, or a labeled use. A single 68-week trial in a 445-participant population with knee osteoarthritis does not establish long-term safety, durability of effect beyond 68 weeks, or generalizability to broader populations without osteoarthritis.
Evidence Context
Retatrutide remains an investigational compound in MitoCore's evidence library, with its evidence base currently built on earlier Phase 2 data. TRIUMPH-4's topline result is consistent with the magnitude of effect seen in retatrutide's earlier trials, but as unreviewed sponsor-reported topline data it does not itself change retatrutide's current evidence grade. Given the trial's size and design, a future evidence-grade review may be warranted once the full peer-reviewed publication is available.
Sources
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