Retatrutide Phase 3: What the 2026 Trial Results Show
Eli Lilly's TRIUMPH Phase 3 programme has delivered the most significant weight loss data ever recorded in a pharmaceutical trial. Here is what researchers need to know about the 2026 results.
The TRIUMPH Phase 3 Programme
Retatrutide (LY3437943) is Eli Lilly's investigational triple hormone receptor agonist, simultaneously targeting GLP-1, GIP, and glucagon receptors. Following exceptional Phase 2 data — up to 24.2% weight reduction at 48 weeks with the 12 mg dose — the compound advanced into the TRIUMPH Phase 3 programme, one of the most closely watched clinical trial programmes in metabolic disease research.
The TRIUMPH programme comprises eight trials across different populations. As of May 2026, results have been reported from TRIUMPH-4 (obesity plus knee osteoarthritis) and TRANSCEND-T2D-1 (type 2 diabetes), with the largest general obesity trials (TRIUMPH-1 and TRIUMPH-2) expected to report in mid-2026.
⚠ All information is presented for research and educational purposes only. Retatrutide is an investigational compound. Not for human consumption. Research use must comply with applicable regulations.
TRIUMPH-4: Weight Loss and Osteoarthritis Outcomes
TRIUMPH-4 is the first Phase 3 trial to report positive topline results, announced by Eli Lilly in December 2025. The trial evaluated retatrutide in adults with obesity or overweight and moderate-to-severe knee osteoarthritis — a population of significant research interest given the mechanical and inflammatory relationship between adiposity and joint disease.
Weight Loss Results
| Dose | Mean Weight Loss | vs Placebo |
|---|---|---|
| Retatrutide 9 mg | −26.4% | −2.1% placebo |
| Retatrutide 12 mg | −28.7% | −2.1% placebo |
The 28.7% figure at 12 mg represents the largest mean weight reduction ever recorded in a Phase 3 pharmaceutical trial at the time of its announcement — surpassing the 22.5% observed with high-dose tirzepatide in SURMOUNT-1 and the 20.9% with semaglutide 2.4 mg in STEP-1.
Osteoarthritis Pain Outcomes
Beyond weight, TRIUMPH-4 demonstrated significant reductions in WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) pain scores:
- •Up to 75.8% reduction in WOMAC pain score
- •More than 1 in 8 participants on retatrutide were completely pain-free at end of trial
- •Researchers attribute this to a combination of mechanical offloading from fat loss and potential direct anti-inflammatory mechanisms
TRANSCEND-T2D-1: Diabetes and Metabolic Control
In March 2026, Eli Lilly reported results from TRANSCEND-T2D-1, evaluating retatrutide in adults with type 2 diabetes:
- •HbA1c reduction: up to −2.0 percentage points
- •Weight loss: up to −16.8%
- •Both endpoints met statistical significance versus placebo
The HbA1c data positions retatrutide as a potential research compound of interest for metabolic dysfunction studies, particularly given the additional glucagon receptor mechanism that may influence hepatic glucose metabolism beyond GLP-1 pathways.
Safety Signals: Dysesthesia
The most notable new safety finding from TRIUMPH-4 was dysesthesia — abnormal skin sensations including tingling, burning, or electric sensations — reported at markedly higher rates than placebo:
| Dose | Dysesthesia Rate |
|---|---|
| 9 mg | 8.8% |
| 12 mg | 20.9% |
| Placebo | 0.7% |
This signal was not prominently identified in Phase 2 data and represents a key monitoring parameter for ongoing TRIUMPH trials. The mechanism is not yet established but is under active investigation.
Gastrointestinal adverse events (nausea 43%, vomiting 21%, diarrhoea 33% at 12 mg) were consistent with the GLP-1 receptor agonist class profile established by semaglutide and tirzepatide.
Remaining TRIUMPH Trials
Seven additional Phase 3 trials are expected to report results across 2026:
- •TRIUMPH-1 — General obesity population (largest trial, expected Q2–Q3 2026)
- •TRIUMPH-2 — Type 2 diabetes (expected Q2–Q3 2026)
- •Additional trials in NASH/MASLD, cardiovascular outcomes, and sleep apnoea
An NDA filing with the FDA is anticipated in Q4 2026, following the completion of the Phase 3 programme.
Retatrutide vs Prior Generation GLP-1 Compounds
| Compound | Mechanism | Peak Phase 3 Weight Loss |
|---|---|---|
| Semaglutide 2.4 mg | GLP-1 monoagonist | ~20.9% (STEP-1) |
| Tirzepatide 15 mg | GLP-1 + GIP dual | ~22.5% (SURMOUNT-1) |
| Retatrutide 12 mg | GLP-1 + GIP + glucagon triple | ~28.7% (TRIUMPH-4) |
The incremental weight loss with each additional receptor target is consistent with the mechanistic hypothesis that broader hormonal pathway engagement produces additive energy expenditure effects.
Disclaimer: This article summarises published clinical trial data for educational and research purposes. Retatrutide is an investigational compound not approved for human therapeutic use. All laboratory research use must comply with applicable regulations and institutional guidelines.
Frequently Asked Questions
TRIUMPH-4 evaluated retatrutide in adults with obesity or overweight and knee osteoarthritis. At 48 weeks, participants on the 9 mg dose achieved mean weight loss of 26.4% and those on the 12 mg dose achieved 28.7%, compared to 2.1% with placebo. These figures represent the largest weight reduction ever recorded in a Phase 3 pharmaceutical trial at the time of publication.
TRIUMPH (Trial Investigating Metabolic and Physiological Outcomes with Retatrutide) is Eli Lilly's Phase 3 development programme for retatrutide. It comprises multiple trials across different patient populations including general obesity (TRIUMPH-1), type 2 diabetes (TRIUMPH-2), and specific co-morbidities such as knee osteoarthritis (TRIUMPH-4). The majority of trials are expected to report results across 2026, with an NDA filing anticipated in Q4 2026.
Dysesthesia — an abnormal, sometimes painful sensation including tingling, burning, or electric-shock-like feelings — was reported in 8.8% of participants on the 9 mg dose and 20.9% on the 12 mg dose, compared to 0.7% in the placebo group. This was a novel safety finding not prominently identified in Phase 2 research and has been flagged as a key monitoring point for ongoing TRIUMPH trials. Gastrointestinal adverse events (nausea 43%, vomiting 21%, diarrhoea 33%) were consistent with the GLP-1 receptor agonist class profile.
Announced in March 2026, TRANSCEND-T2D-1 evaluated retatrutide in people with type 2 diabetes. The trial demonstrated up to 2.0% reduction in HbA1c and 16.8% body weight loss, providing evidence of dual glycaemic control and weight reduction in a diabetic population. This distinguishes retatrutide's research profile from semaglutide, which produces more modest weight loss in diabetic cohorts.
Semaglutide is a GLP-1 receptor monoagonist. Tirzepatide adds GIP receptor agonism, making it a dual agonist. Retatrutide adds glucagon receptor agonism to both, making it a triple agonist (GLP-1, GIP, and glucagon). Glucagon receptor activation is studied for its role in hepatic glucose output modulation, thermogenesis, and energy expenditure — mechanisms distinct from GLP-1 or GIP signalling alone. In preclinical models, triple receptor engagement produces energy expenditure profiles not observed with dual or single agonism.
Based on the Phase 3 programme timeline, Eli Lilly has indicated an NDA (New Drug Application) filing with the FDA in Q4 2026. Regulatory review typically takes 6 to 12 months, placing potential approval in 2027. For research purposes, retatrutide remains available as a research-grade compound from approved suppliers. All research use must comply with applicable laboratory regulations.
References
- 1.Eli Lilly and Company. “Lilly's triple agonist, retatrutide, delivered weight loss of up to an average of 71.2 lbs along with substantial relief from osteoarthritis pain in first successful Phase 3 trial.” Eli Lilly Press Release (2025). https://investor.lilly.com/news-releases/news-release-details/lillys-triple-agonist-retatrutide-delivered-weight-loss-average
- 2.Jastreboff AM, Aronne LJ, Ahmad NN, et al. “Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial.” New England Journal of Medicine (2023). https://www.nejm.org/doi/full/10.1056/NEJMoa2301972
- 3.Coskun T, Urva S, Roell WC, et al. “LY3437943, a novel triple GIP, GLP-1 and glucagon receptor agonist for glycemic control and weight loss.” Cell Metabolism (2022). https://pubmed.ncbi.nlm.nih.gov/36195100/
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