Retatrutide
The investigational triple agonist drawing attention for weight loss that has reached territory once associated mainly with bariatric surgery.
What It Is
Retatrutide (LY3437943) is a once-weekly investigational molecule that activates three metabolic hormone receptors at once: GIP, GLP-1 and glucagon. It is being developed by Eli Lilly for obesity and several obesity-related conditions.
The Weight-Loss Numbers
Phase 2 reached 24.2% average weight loss at 48 weeks in the 12 mg group.
Human Phase 2TRIUMPH-1 reported 28.3% / 70.3 lb average loss at 80 weeks with 12 mg.
Phase 3 toplineIn Phase 2, 26% of the 12 mg group lost at least 30% of body weight by week 48.
Human Phase 2Phase 3 programs have also reported improvements in OSA, knee-OA pain and glycemic outcomes.
Phase 3 toplineWhy “Triple Agonist” Matters
Semaglutide targets GLP-1. Tirzepatide targets GIP + GLP-1. Retatrutide adds glucagon-receptor activity to the mix. That extra pathway is why it is often described as the next step in incretin-based obesity pharmacology and why people are curious about whether it can push weight loss, energy expenditure and metabolic changes further.
Three Receptors, One Molecule
GLP-1 and GIP signaling influence appetite, satiety, insulin secretion and glucose control. Glucagon signaling can increase hepatic energy mobilization and may contribute to energy expenditure. Retatrutide is engineered so the clinical effect comes from the balance of all three receptor activities.
Human Trial Results
In the peer-reviewed Phase 2 obesity trial, average body-weight change at 48 weeks was −17.1% with combined 4 mg groups, −22.8% with combined 8 mg groups and −24.2% with 12 mg, compared with −2.1% with placebo.
Lilly reported in May 2026 that TRIUMPH-1 participants assigned to 12 mg lost an average of 28.3% (70.3 lb) at 80 weeks, and 45.3% achieved at least 30% weight loss. A prespecified extension in participants with baseline BMI ≥35 reported 30.3% (85.0 lb) average loss at 104 weeks.
Still Investigational
Retatrutide is not FDA approved. Gastrointestinal adverse effects such as nausea, diarrhea, vomiting and constipation are prominent in incretin trials, and dose-dependent heart-rate increases were observed in Phase 2. Long-term labeling, contraindications and final prescribing guidance do not yet exist.
How It Has Been Studied
The Phase 2 obesity study tested target doses of 1, 4, 8 and 12 mg once weekly, with some groups using lower starting doses and stepwise escalation. Phase 3 trials use structured titration under trial supervision. Those are clinical-trial designs, not an approved public-use protocol.