Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial

This phase 2 clinical trial, published in the New England Journal of Medicine, evaluated the efficacy and safety of retatrutide, the first triple agonist of GIP, GLP-1, and glucagon receptors, for the treatment of obesity. The randomized, double-blind, placebo-controlled study included 338 adults with obesity (BMI >=30) or overweight with comorbidity, without type 2 diabetes.

Participants were randomized to different doses of retatrutide (1, 4, 8, or 12 mg) or placebo administered subcutaneously weekly for 48 weeks. Dose escalation schedules varied to optimize gastrointestinal tolerability.

The results were unprecedented in the history of pharmacological obesity treatment:

• At the highest dose (12 mg), mean weight loss was 24.2% at 48 weeks
• In the 8 mg group, the reduction was 22.8%
• Approximately 100% of participants in the 12 mg group lost at least 5% of body weight
• 83% in the 12 mg group lost at least 15% of body weight
• The weight loss curve showed no plateau at 48 weeks, suggesting potential for further reduction

These results represented the greatest weight loss ever demonstrated with any anti-obesity drug in a clinical trial up to the publication date. The triple mechanism of action offers theoretical advantages: GLP-1 agonism reduces appetite and delays gastric emptying, GIP agonism potentiates metabolic effects, and glucagon agonism increases energy expenditure and lipid oxidation. The most common adverse effects were gastrointestinal (nausea, diarrhea, vomiting), mostly mild to moderate.