Trial design
TRIUMPH-1 randomized 2,026 adults with BMI ≥30 (or ≥27 with weight-related comorbidities) to receive retatrutide 4 mg, 8 mg, 12 mg, or placebo once weekly subcutaneously for 80 weeks, plus a 24-week extension cohort. The primary endpoint was percent change in body weight from baseline. Co-primary: proportion achieving ≥5% weight reduction.
| Dose arm | Mean change in body weight | Achieved ≥10% WL | Achieved ≥20% WL |
|---|---|---|---|
| Placebo | -2.4% | 11.5% | 1.2% |
| Retatrutide 4 mg | -16.1% | 78.4% | 31.8% |
| Retatrutide 8 mg | -22.8% | 89.2% | 71.4% |
| Retatrutide 12 mg | -28.3% | 93.6% | 83.1% |
How retatrutide is different from semaglutide and tirzepatide
Retatrutide adds a third receptor to the dual mechanism of tirzepatide. The hypothesis: glucagon receptor activation enhances energy expenditure (thermogenesis, lipolysis) on top of the appetite-suppressing and glucose-regulating effects already produced by GLP-1 + GIP agonism. Whether this proves out in long-term cardiometabolic outcomes is still an open question — TRIUMPH-OUTCOMES is enrolling now.
| Molecule | Receptors | Mean weight loss | FDA status (May 2026) |
|---|---|---|---|
| Semaglutide | GLP-1 (single) | -14.9% (STEP-1, 68wk) | Approved 2021 (Wegovy) |
| Tirzepatide | GLP-1 + GIP (dual) | -20.9% (SURMOUNT-1, 72wk) | Approved 2023 (Zepbound) |
| Retatrutide | GLP-1 + GIP + glucagon (triple) | -28.3% (TRIUMPH-1, 80wk) | Investigational |
Safety and tolerability
The side-effect profile of retatrutide resembles other GLP-1 receptor agonists — predominantly gastrointestinal, dose-dependent, transient during titration. Notable findings from TRIUMPH-1:
- Nausea: 41.2% (12 mg) vs 7.8% (placebo); typically resolves by week 12
- Vomiting: 19.4% (12 mg) vs 2.1% (placebo)
- Diarrhea: 28.5% (12 mg) vs 7.9% (placebo)
- Discontinuation for adverse events: 14.1% (12 mg) vs 4.2% (placebo) — higher than tirzepatide (6.0% in SURMOUNT-1)
- Heart rate increase: mean +3-4 bpm at 12 mg, possibly related to glucagon-receptor activation
- No pancreatitis signal at adjudicated review; no thyroid C-cell tumor signal in 80 weeks
Approval timeline and what comes next
Eli Lilly filed for FDA approval in June 2026 following TRIUMPH-1. Approval is expected late 2026 to mid-2027. The TRIUMPH-OUTCOMES cardiovascular outcomes trial (n=14,400) is enrolling, with primary readout in 2029. Compounded retatrutide is not legal: retatrutide is not on the FDA Section 503A or 503B bulk drug substances list, and the API is not commercially available from compliant suppliers. Patients should be cautious of telehealth companies advertising "retatrutide" — most are research-grade peptides sold via offshore channels and outside the legitimate compounding framework.
Implications for compounded GLP-1 patients today
If you're on compounded semaglutide or tirzepatide today, retatrutide is not a near-term replacement option (no legal compounding pathway). The 2027-2028 launch will likely follow the same trajectory as Zepbound: a brand-only launch through traditional pharmacies, dose-escalation supply constraints, and a high cash-pay price ($1,000+/month initially) before competitive pressure brings it down. For patients optimizing today, tirzepatide remains the higher-efficacy compounded option ($186/mo flat-rate at NexLife on the 12-month plan); semaglutide remains the deeper-evidence option for cardiovascular outcomes (SELECT trial).