Retatrutide

Investigated uses

• Obesity, overweight with comorbidity, type 2 diabetes, sleep apnea, osteoarthritis and other obesity-related conditions in clinical development.

Mechanism and hypotheses

• Retatrutide is a once-weekly investigational agonist of GIP, GLP-1 and glucagon receptors.
• Hypothesized: Its clinical weight-loss effect likely reflects reduced intake plus glucagon-linked energy-expenditure pathways, but the contribution of each receptor remains under study.

Human evidence

• In a phase 2 trial of 338 adults, mean weight change at 48 weeks ranged from −8.7% at 1 mg to −24.2% at 12 mg, versus −2.1% with placebo. Limitations: Phase 2, 48 weeks, sponsor-manufactured product; no approved indication or long-term rare-event estimate.
• In the peer-reviewed phase 3 TRANSCEND-T2D-1 trial, 537 adults with early type 2 diabetes inadequately controlled by diet and exercise were randomized to retatrutide 4 mg, 9 mg or 12 mg weekly or placebo for 40 weeks. Retatrutide reduced HbA1c and body weight more than placebo across all active arms. Limitations: The study evaluated sponsor-manufactured retatrutide as monitored monotherapy in a selected early-diabetes population; 40 weeks is insufficient for uncommon or long-latency harms, and the results do not validate gray-market products.
• Lilly disclosed phase 3 topline results from TRIUMPH-1, TRIUMPH-2, TRIUMPH-3 and TRIUMPH-4 during December 2025–July 2026; TRIUMPH-1 was presented at ADA 2026, while detailed TRIUMPH-2 and TRIUMPH-3 results had not yet been peer reviewed at the review date. Limitations: Sponsor topline reporting is provisional and does not replace full peer review, independent replication, regulatory review, or rare-event surveillance. It does not validate any product sold as retatrutide outside the trials.

Safety highlights

• Gastrointestinal events—especially nausea, diarrhea, vomiting and constipation—were most common and dose-related in phase 2.
• Long-term rare risks, cardiovascular outcomes and risks specific to glucagon-receptor activation remain investigational.

Regulatory context

Retatrutide remains investigational and is not FDA approved. Lilly states that it is not available for public use outside clinical trials.