Randomised controlled trials
In the trials below, people were assigned at random to take Tirzepatide or a dummy pill (placebo). All the weight loss figures are averages: how much body weight fell from the start.
| Trial | Key result | Source |
|---|---|---|
| [1]SURMOUNT-1 | Up to 20.9% average weight loss at the highest dose (15 mg). About 9 in 10 people lost ≥5% of body weight; more than half lost ≥20%. Discontinuation due to side effects: 4.3–7.1% vs. 2.6% placebo. | New England Journal of Medicine 2022 ↗ |
| [2]SURMOUNT-3 | Additional 18.4% mean weight loss after the initial lifestyle-induced loss — total mean loss of ~26% from original baseline. | Nature Medicine 2024 ↗ |
| [3]SURMOUNT-4 | 25.3% total weight loss over the full 88-week period. Stopping drug led to 14.0% weight regain vs. 5.5% additional loss in those who continued. | JAMA 2024 ↗ |
| [4]SURMOUNT-5 (head-to-head vs. semaglutide) | Tirzepatide was superior to semaglutide 2.4 mg on body weight reduction and waist circumference — the first direct head-to-head superiority trial between these two drugs. | New England Journal of Medicine 2025 ↗ |
| [5]SURMOUNT-1 Body Composition Substudy | ~75% of weight lost was fat mass, ~25% lean mass. Total lean mass change: –10.9% tirzepatide vs. –2.6% placebo. | Obesity 2024 ↗ |
Reported side effects
The rates below come from the SURMOUNT-1 trial. View source
| Side effect | Frequency in trial |
|---|---|
| Nausea | 31% |
| Diarrhoea | 23% |
| Vomiting | 18% |
| Constipation | 12% |
| Decreased appetite | 19% |
Body composition data
In a body composition substudy of SURMOUNT-1 (n=160, DXA scans at 72 weeks), approximately 75% of weight lost was fat mass and 25% was lean mass — consistent with other weight loss interventions. Total lean mass change was –10.9% with tirzepatide vs. –2.6% with placebo.
Heart and metabolic data
Improvements in systolic/diastolic blood pressure, triglycerides, LDL, and HbA1c across SURMOUNT trials. Reduced sleep apnoea severity (SURMOUNT-OSA). Reduced liver fat in NASH (SYNERGY-NASH phase 2). A dedicated cardiovascular outcomes trial (SURPASS-CVOT) is ongoing.