SURMOUNT-1 Trial: Landmark Results Showing 22.5% Body Weight Reduction

The SURMOUNT-1 trial, published in the New England Journal of Medicine in July 2022, was a landmark study that demonstrated tirzepatide's remarkable efficacy for weight management in adults with obesity or overweight.

Study Design

• Type: Phase 3, randomized, double-blind, placebo-controlled
• Duration: 72 weeks
• Participants: 2,539 adults with BMI ≥30, or BMI ≥27 with at least one weight-related complication (excluding diabetes)
• Treatment Groups: Tirzepatide 5 mg, 10 mg, or 15 mg vs. placebo, all once weekly
• Primary Endpoints: Percent change in body weight and proportion achieving ≥5% weight loss

Key Results

Average Weight Loss by Dose

• Tirzepatide 5 mg: -15.0% body weight (-34.4 lbs average)
• Tirzepatide 10 mg: -19.5% body weight (-49.1 lbs average)
• Tirzepatide 15 mg: -20.9% body weight (-52.0 lbs average)
• Placebo: -3.1% body weight

Using the treatment policy estimand (which includes all participants regardless of adherence):

• Tirzepatide 15 mg: -22.5% in the efficacy estimand analysis

Proportion Achieving Weight Loss Thresholds

At the 15 mg dose:

• ≥5% weight loss: 91% (vs. 35% placebo)
• ≥10% weight loss: 79% (vs. 14% placebo)
• ≥15% weight loss: 66% (vs. 5% placebo)
• ≥20% weight loss: 50% (vs. 3% placebo)
• ≥25% weight loss: 33% of participants

Metabolic Improvements

Beyond weight loss, SURMOUNT-1 demonstrated significant metabolic benefits:

• Waist circumference: Reduced by 14.5 cm (15 mg)
• Blood pressure: Systolic BP reduced by 7.2 mmHg
• Lipid improvements: Significant reductions in triglycerides; increases in HDL cholesterol
• Inflammatory markers: Reductions in high-sensitivity CRP
• Fasting insulin: Reduced by 54.8% (15 mg)

Safety Profile

The most common adverse events were gastrointestinal:

• Nausea: 24-31% (vs. 9.5% placebo)
• Diarrhea: 18-23% (vs. 7.3% placebo)
• Constipation: 11-17% (vs. 4.8% placebo)
• Vomiting: 6-13% (vs. 2.8% placebo)

Most GI events were mild to moderate and occurred primarily during dose escalation. Discontinuation due to adverse events was 4.3-7.1% across tirzepatide groups vs. 2.6% for placebo.

Clinical Significance

SURMOUNT-1 established tirzepatide as the most effective anti-obesity medication studied to date in a Phase 3 trial. The average weight loss of ~20% at the highest dose approaches results previously only achievable through bariatric surgery.

These results directly led to the FDA approval of Zepbound (tirzepatide) for chronic weight management in November 2023.