Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1) — VialBase Research

Summary

SURMOUNT-1 was the landmark phase 3 trial of tirzepatide for obesity in adults without diabetes. As a dual GIP/GLP-1 receptor agonist, tirzepatide demonstrated weight loss exceeding that seen in any prior pharmacotherapy trial, with mean losses up to 22.5% at the highest dose. This trial established tirzepatide as a step-change in obesity pharmacotherapy.

Key Findings

• Mean weight loss at 72 weeks: -15.0% (5mg), -19.5% (10mg), -20.9% (15mg) vs -3.1% (placebo)
• At 15mg dose: 96% achieved ≥5% weight loss, 63% achieved ≥20% weight loss
• Significant improvements in all cardiometabolic parameters (waist, BP, lipids, insulin sensitivity)
• GI adverse events most common (nausea, diarrhea, constipation), mostly mild-moderate and transient
• Dose-dependent efficacy across all three dose levels
• Discontinuation due to AEs: 4.3-7.1% (tirzepatide) vs 2.6% (placebo)

Methodology

Double-blind, placebo-controlled, multicenter RCT in 2,539 adults with BMI ≥30 (or ≥27 with comorbidity) without diabetes. Randomized 1:1:1:1 to tirzepatide 5mg, 10mg, 15mg, or placebo once weekly. 72-week treatment period with 20-week dose escalation. Lifestyle intervention in all arms.

Limitations

• No active comparator (no head-to-head with semaglutide in this trial)
• Predominantly White participants (71%)
• Does not address weight maintenance after discontinuation
• Long dose escalation period (20 weeks to reach 15mg)
• Gallbladder-related adverse events observed at higher rates

Relevance to Content

The most important tirzepatide trial for obesity content. The ~20-22% weight loss represents a significant advance over semaglutide’s ~15% (STEP 1). Essential citation for any comparison content or articles positioning tirzepatide as “next-generation” GLP-1 therapy. The dual-agonist mechanism is a key differentiator.

See Also

• Parent compound: Tirzepatide
• Semaglutide