In TRIUMPH-5, how many percentage points more body weight will participants lose on retatrutide than on tirzepatide at week 80?

My most likely value for retatrutide’s weight loss advantage over tirzepatide at week 80 in TRIUMPH-5 is 4.2 percentage points, anchored by the 4.1-point gap between TRIUMPH-1 and SURMOUNT-1.

TRIUMPH-5 (NCT06662383) is Eli Lilly's Phase 3, randomized, double-blind head-to-head trial of retatrutide (a GIP/GLP-1/glucagon triple agonist) versus tirzepatide (Zepbound/Mounjaro), both at maximum tolerated dose, in about 800 adults with obesity with or without type 2 diabetes. The primary endpoint is percent change in body weight from baseline to week 80; ClinicalTrials.gov lists estimated primary completion in November 2026. In TRIUMPH-1 (topline May 2026), retatrutide 12 mg produced 28.3% mean weight loss at 80 weeks (about 25.0% on a treatment-regimen basis). In SURMOUNT-1, tirzepatide 15 mg produced 22.5% mean weight loss at 72 weeks. Lilly plans to submit retatrutide to the FDA in Q1 2027. The size of the gap determines whether retatrutide becomes a premium successor to tirzepatide or mainly cannibalises it.

Resolves to the difference in mean percent change in body weight from baseline to week 80 between the retatrutide arm and the tirzepatide arm in TRIUMPH-5, expressed in percentage points as retatrutide weight loss minus tirzepatide weight loss (a positive value means retatrutide produced more weight loss), as first disclosed by Eli Lilly in a press release, earnings materials, a conference presentation or a peer-reviewed publication. Use the treatment-regimen estimand if Lilly reports it; otherwise use the efficacy estimand. If Lilly reports only each arm's mean percent change, compute the difference. If there is more than one retatrutide arm, use the highest-dose arm. If no week-80 results are disclosed by 31 December 2027, the question is annulled.