Retatrutide

Triple GLP-1/GIP/glucagon receptor agonist in clinical development - the biggest weight-loss signal seen in Phase 2 to date.

InvestigationalNot approvedInjectableMetabolic

Key facts

Common routesSubcutaneous

Half-life~6 days

Typical range1-12 mg/week

Summary

Retatrutide (LY3437943, Eli Lilly) is a once-weekly triple agonist at GLP-1, GIP, and glucagon receptors. GLP-1/GIP drive satiety and glycemic control; the added glucagon activity pushes energy expenditure and fat oxidation. In the Phase 2 obesity trial, 48-week weight-loss numbers at the top dose exceeded anything previously published in the incretin class.

Status: not yet approved. The Phase 3 cardiovascular/kidney outcomes trial TRIUMPH-Outcomes (NCT06383390) is recruiting, but multi-year outcomes and post-marketing data don't exist yet. Until they do, the risk/benefit profile carries more uncertainty than tirzepatide or semaglutide.

Mechanism notes

GLP-1 receptor activation

Reduces appetite, slows gastric emptying, and boosts glucose-dependent insulin secretion - the same core mechanism as semaglutide.

GIP receptor activation

Layers in additional incretin signaling, supports insulin sensitivity, and can blunt some GLP-1-typical nausea - the tirzepatide piece.

Glucagon receptor activation

The real differentiator. Increases energy expenditure and lipolysis - explains the larger weight-loss magnitude, but also raises resting heart rate and the overall "activation" profile.

Dosing patterns

Phase 2 titration schedule

Trials escalated once-weekly dosing from low mg up to 12 mg, with monthly step-ups. As with tirzepatide, GI tolerability scales directly with how fast you titrate - don't rush it.

Use outside clinical trials

No FDA product means no standardized dosing, no purity control, and no clinical monitoring. Anecdotal protocols vary widely; potency and quality carry no regulatory guarantee.

Evidence snapshot

The evidence base is strong at Phase 2: Jastreboff et al. (2023) showed dose-dependent weight loss in obesity over 48 weeks. A Phase 2a MASLD/MASH trial supports broader metabolic effects beyond pure weight loss. The large Phase 3 outcomes trial (TRIUMPH-Outcomes, NCT06383390) is underway.

Phase 2 trials

Largest published incretin-class weight-loss signal over 48 weeks; MASLD/MASH data suggests broader metabolic effects.

TRIUMPH-Outcomes (Phase 3)

Event-driven RCT with ~10,000 participants targeting MACE and kidney endpoints in adults with BMI ≥27 and ASCVD and/or CKD. Recruiting; no results yet.

Safety considerations

The incretin-class side-effect profile (nausea, vomiting, diarrhea/constipation) plus the glucagon-driven activation signal: resting heart-rate increases have been reported consistently. Risk management leans on slow titration, intentional nutrition (protein especially), and monitoring.

Key cautions

Investigational only - no FDA approval; long-term safety data is still being established
Glucagon receptor activity can raise resting heart rate; monitor HR and blood pressure
Aggressive GI side effects if titration is rushed; dose escalation is not optional