Retatrutide 2026: Phase 3 Trials and What Researchers Should Know

The Phase 2 trial of Retatrutide published in the New England Journal of Medicine in June 2023 was a 48-week, randomised, double-blind, placebo-controlled study evaluating five dose levels (1mg, 4mg, 8mg, 12mg per week) in adults with a BMI of 27–50 without diabetes. Key findings at the highest dose:

• Mean body weight reduction of approximately 22.8% at 48 weeks
• Dose-dependent response across all dose levels
• Reductions in waist circumference, triglycerides, blood pressure, and fasting glucose
• Adverse events consistent with the GLP-1 class (nausea, vomiting, constipation), predominantly mild-to-moderate and dose-dependent

The 22.8% mean weight reduction at 48 weeks was notable: most GLP-1 monotherapy trials achieve 12–15% at similar timeframes. The triple-receptor mechanism appeared to produce an additive effect beyond what dual agonism (Tirzepatide) achieves.

Eli Lilly initiated Phase 3 evaluation of Retatrutide under the programme designation TRIUMPH. The programme includes multiple trials:

• TRIUMPH-1 — obesity without diabetes, evaluating 12mg/week vs placebo over 72 weeks (primary endpoint: percentage weight change)
• TRIUMPH-2 — obesity with type 2 diabetes, evaluating both weight and glycaemic endpoints
• TRIUMPH-3 — cardiovascular outcomes trial in high-risk patients (long-term safety and MACE)

Enrolment for TRIUMPH-1 and TRIUMPH-2 was underway as of late 2024, with primary completion expected in 2026–2027. Regulatory submissions and potential approvals are estimated post-2027, pending trial outcomes.

For preclinical and mechanistic researchers, Retatrutide's Phase 3 progression has several implications:

Benchmark data availability: Phase 2 data provides robust dose-response characterisation that can inform preclinical protocol design. The 12mg dose is the primary Phase 3 dose, having demonstrated the best efficacy-tolerability balance.

Triple-agonist mechanism research: With Phase 3 underway, interest in isolating the specific contributions of glucagon receptor co-agonism (versus GLP-1/GIP alone) has intensified. Tirzepatide represents the GLP-1/GIP control condition in such comparisons.

Weight nadir and durability: One open question Phase 3 will address is whether the weight trajectory plateaus earlier with triple agonism or continues to decline beyond 48 weeks. Phase 2 was not long enough to fully characterise this.

For Australian researchers requiring Retatrutide for laboratory studies, supply availability has improved in 2025–2026 as manufacturing scale-up for Phase 3 support has increased synthetic peptide production capacity globally. RetaLABS stocks research-grade Retatrutide with COA documentation available on request. All products are for laboratory research use only.