Retatrutide — Triple GLP-1/GIP/glucagon receptor agonist

TRIUMPH Phase 2 trial (NEJM, 2023): 12mg retatrutide achieved 24.2% weight reduction at 48 weeks — the highest weight loss ever recorded for any pharmacotherapy in a Phase 2 trial (surpassing tirzepatide's 22.5%). The glucagon component also produced significant reductions in liver fat (>50% reduction in hepatic steatosis). The key mechanistic advantage over tirzepatide is increased energy expenditure (thermogenesis) in addition to reduced intake. The main safety concern is glucagon-mediated tachycardia; mean HR increase of ~5-8 bpm at highest doses. If Phase 3 data replicates Phase 2 findings, retatrutide may set a new benchmark for pharmacological weight management.

Overview

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Compound Class

Triple GLP-1/GIP/glucagon receptor agonist

Mechanism of Action

Retatrutide is the first-in-class triple incretin agonist, simultaneously activating GLP-1, GIP, and glucagon receptors. The glucagon component critically distinguishes it from tirzepatide (dual GIP/GLP-1 only): hepatic glucagon receptor activation drives direct fat oxidation, increases energy expenditure through brown adipose tissue thermogenesis, and reduces hepatic steatosis independent of caloric restriction. GLP-1 receptor activation: appetite suppression, gastric emptying delay. GIP receptor activation: enhanced insulin sensitivity, reduced GLP-1 side effects. Glucagon receptor activation: fat oxidation, thermogenesis, direct lipolysis. The combination produces greater weight loss than any currently approved pharmacotherapy by simultaneously reducing intake AND increasing expenditure.

Regulatory Status

Investigational — Phase 3 TRIUMPH trials ongoing (2024-2026)

Evidence Level

Moderate — Phase 2 completed (n=338, TRIUMPH trial); Phase 3 ongoing