Retatrutide Delivers 28% Weight Loss in TRIUMPH-1 Phase 3 Trial

Retatrutide is administered as a subcutaneous injection in clinical trials.

TRIUMPH-1 Results Show Significant Weight Reduction

Eli Lilly has announced topline results from its Phase 3 TRIUMPH-1 clinical trial, revealing that the investigational triple hormone receptor agonist retatrutide achieved an average weight loss of 28.3% — approximately 70.3 pounds — at 80 weeks in adults with obesity or overweight with at least one weight-related comorbidity, according to the company's press release. The trial met all primary and key secondary endpoints across all tested doses.

The magnitude of weight loss observed in the trial approaches results historically associated with bariatric surgery. According to Eli Lilly, 45.3% of participants receiving the highest dose achieved a body weight reduction of 30% or more, a threshold that has traditionally required surgical intervention.

Dose-Response Data Across Three Arms

The TRIUMPH-1 trial evaluated three dose levels, each showing clinically meaningful results, as reported by AJMC and Clinical Trials Arena:

• 12 mg dose: Average weight loss of 28.3% (approximately 70.3 pounds) at 80 weeks
• 9 mg dose: Average weight loss of 25.9% (approximately 64.4 pounds) at 80 weeks
• 4 mg dose: Average weight loss of 19.0% (approximately 47.2 pounds) at 80 weeks

In a prespecified extension involving participants with a baseline BMI of 35 or higher, those who continued and tolerated the 12 mg dose achieved an average weight loss of 30.3% — approximately 85 pounds — at 104 weeks, according to Eli Lilly.

How Retatrutide Works: A Triple-Agonist Approach

Retatrutide is a first-in-class molecule designed to simultaneously activate three metabolic hormone receptors: GLP-1, GIP, and glucagon. According to researchers, this triple-agonist mechanism may produce synergistic metabolic effects that go beyond what current dual-agonist therapies like tirzepatide options can achieve.

• GLP-1 receptor agonism may suppress appetite, slow gastric emptying, and enhance insulin secretion
• GIP receptor agonism may improve insulin sensitivity and contribute to satiety
• Glucagon receptor agonism may increase energy expenditure, promote thermogenesis, and support fat oxidation

This approach represents a potential evolution in the obesity treatment landscape, building on the success of semaglutide treatment programs and other GLP-1 receptor agonists already in clinical use.

Safety Profile and Cardiometabolic Benefits

According to trial data reported by Eli Lilly, the most common adverse events were gastrointestinal in nature, including nausea, diarrhea, constipation, and vomiting. Some participants also reported dysesthesia, described as an abnormal skin sensation such as burning or tingling. Discontinuation rates due to adverse events were 11.3% for the 12 mg dose, 6.9% for the 9 mg dose, and 4.1% for the 4 mg dose.

Beyond weight loss, the trial showed significant improvements in several cardiovascular and metabolic risk factors, including:

• Waist circumference
• Non-HDL cholesterol and triglycerides
• Systolic blood pressure
• High-sensitivity C-reactive protein (hs-CRP), an inflammatory marker

What Comes Next for Retatrutide

Full TRIUMPH-1 data are expected to be presented at the American Diabetes Association's 86th Scientific Sessions in June 2026, alongside results from the TRANSCEND-T2D-1 trial evaluating retatrutide in adults with type 2 diabetes. Retatrutide remains an investigational medication and has not yet received regulatory approval from the FDA or any other agency.

For individuals interested in currently available GLP-1-based treatments, it may be worth exploring whether you qualify for existing programs.

This article is for informational purposes only and is not medical advice. Consult your healthcare provider before starting any weight loss medication or treatment.