TRIUMPH-1 (NCT05929066) is the pivotal general-obesity trial in Eli Lilly's Phase 3 programme for retatrutide, an investigational triple agonist that activates the GIP, GLP-1 and glucagon receptors. Topline results were announced in May 2026; the full, peer-reviewed analysis was published in the New England Journal of Medicine on 29 September 2026.
What the trial tested
TRIUMPH-1 randomised 2,339 adults with obesity or overweight and at least one weight-related comorbidity, but without type 2 diabetes, to once-weekly retatrutide at 4 mg, 9 mg or 12 mg, or placebo. The primary endpoint was change in body weight at 80 weeks.
Weight-loss results
At 80 weeks, the 12 mg group achieved a mean body-weight reduction of 28.3%, or 70.3 lb (31.9 kg), from a baseline average of 248.5 lb and a baseline BMI of 40.0 kg/m². The 9 mg group lost a mean 25.9% and the 4 mg group 19.0%. Within the 12 mg arm, 45.3% of participants lost at least 30% of body weight, and 65.3% finished below the BMI 30 threshold used to define obesity.
A prespecified, blinded extension followed 532 participants with a baseline BMI of at least 35 kg/m² out to 104 weeks. Among those originally assigned to 12 mg, weight loss continued, reaching a mean 30.3%, or 85.0 lb, by week 104.
Cardiometabolic findings
The 12 mg group recorded a mean waist-circumference reduction of 24.1 cm, alongside improvements in non-HDL cholesterol, triglycerides, systolic blood pressure and high-sensitivity C-reactive protein. TRIUMPH-1 was not designed to test cardiovascular outcomes, and no such claim can be drawn from it.
Tolerability
Adverse events were dominated by the gastrointestinal effects typical of the incretin class. At 12 mg, nausea was reported by 42.4% of participants (against 14.8% for placebo), diarrhoea by 32.0%, constipation by 26.1% and vomiting by 25.3%. Discontinuation because of adverse events rose with dose: 4.1% at 4 mg, 6.9% at 9 mg and 11.3% at 12 mg, against 4.9% for placebo.
What this does and does not change
Retatrutide is investigational. It is not licensed by the MHRA and is not available on the NHS; Lilly has said it intends to file for approval early in 2027. For laboratory research compounds, nothing here alters the position under the Medicines Act 1968 and the Human Medicines Regulations 2012: unlicensed peptides remain research-use-only and are not medicines.
This article records trial findings for research and educational purposes. It is not medical advice.
This article is AI-researched and editorially reviewed. It is provided for research and educational purposes only and is not medical advice. Research peptides are not licensed for human consumption in the UK.