Retatrutide Phase 3 Trials
What's Next & When

Phase 1 — Safety & Dosing

Eli Lilly ran first-in-human Phase 1 trials establishing the safety profile, pharmacokinetics (drug behavior in the body), and dose-finding for Retatrutide. Published preclinical and Phase 1 results confirmed the triple-agonist mechanism was functional and the compound was safe enough to advance to efficacy testing.

Phase 2 — The Record-Breaking Results (NEJM June 2023)

338 adults randomized across six active dose arms and placebo. 48 weeks total (24-week escalation + 24-week maintenance). Results published June 2023 in the New England Journal of Medicine, authored by Jastreboff et al.

• 24.2% mean body weight reduction at 12 mg — highest ever recorded pharmacologically
• More than 40% of participants achieved ≥25% body weight loss
• 17.5 cm mean waist circumference reduction
• 46% liver fat reduction in metabolic syndrome subgroup
• No weight loss plateau at trial end — still declining at 48 weeks
• Broadly favorable safety profile consistent with GLP-1 class

Phase 3 — TRIUMPH Program (Multiple Trials)

Eli Lilly's Phase 3 program for Retatrutide is known as TRIUMPH (Triple Hormone Receptor Agonist for Metabolic diseases Program). Multiple concurrent trials running across several indications:

• TRIUMPH-1 (Obesity — primary registration trial): The core obesity Phase 3 trial comparing 12 mg Retatrutide vs placebo over 72 weeks in adults with BMI ≥30 or ≥27 with comorbidities. Primary endpoint: ≥5% body weight loss vs placebo. Expected enrollment: ~2,000–3,000 participants.
• TRIUMPH-2 (Type 2 Diabetes): Evaluating Retatrutide for glycemic control in T2D patients — HbA1c reduction as primary endpoint alongside weight loss.
• TRIUMPH-NASH: Dedicated liver disease trial focused on MASH (formerly NASH) resolution and fibrosis improvement. The 46% Phase 2 liver fat result made this an obvious Phase 3 target.
• TRIUMPH-CVOT (Cardiovascular Outcomes Trial): Testing whether Retatrutide reduces MACE (major adverse cardiovascular events) in high-risk patients — similar to the SELECT trial for semaglutide and SURMOUNT-CVOT for tirzepatide.
• TRIUMPH-Sleep: Evaluating effects on obesity-related sleep apnea — driven by the recognition that significant weight loss often resolves OSA.

Phase 3 Completion & Data Readout

Based on typical Phase 3 trial timelines for GLP-1 class drugs (72–96 weeks of treatment plus enrollment and follow-up), primary Phase 3 data readouts for the obesity indication are projected in 2026–2027. If Phase 2 trajectory holds through 72 weeks, Phase 3 mean weight loss could approach or exceed 30%.

The key scientific question for Phase 3: does the weight loss curve continue declining, plateau, or accelerate further when maintained at full dose through 72+ weeks? The Phase 2 data suggests continued decline — but Phase 3 will definitively answer this.

FDA Submission & Approval

Following successful Phase 3 data readouts, Eli Lilly would file a New Drug Application (NDA) with the FDA. The FDA's standard review process takes 10–12 months for a Priority Review designation (which Retatrutide is likely to receive given its breakthrough efficacy profile). This places the earliest plausible FDA approval in the 2027–2028 timeframe.

Note: Breakthrough Therapy Designation (BTD) from the FDA can accelerate this timeline. Based on Phase 2 results, Retatrutide appears a strong candidate for BTD.

Commercial Launch

Following FDA approval, Eli Lilly would launch Retatrutide commercially under a brand name (yet to be announced). Pricing is expected to be competitive with or exceed tirzepatide (Zepbound, ~$549–$1,000/month without insurance). Insurance coverage timelines and coverage decisions will shape real-world access.

For researchers, the commercial approval of Retatrutide will validate years of preclinical and translational research that relied on research-grade supply from suppliers like QSC Peptides.