Evidence review
What clinical trials report for GLP-1 weight loss in 2026, from STEP and SURMOUNT to the latest head-to-head and oral-drug data.
Published June 1, 2026 · GLP1 One Telehealth Editorial Team
Across pivotal trials, semaglutide produced about 15% average weight loss (STEP 1) and tirzepatide up to about 21% (SURMOUNT-1) over 68–72 weeks with lifestyle support. The 2025 head-to-head SURMOUNT-5 trial put tirzepatide at 20.2% vs semaglutide 13.7%. Real-world results are usually lower, driven by adherence and support.
Educational use only. This article is for educational purposes only and does not provide medical advice. Compounded semaglutide and compounded tirzepatide are not FDA-approved finished drug products and should only be prescribed when clinically appropriate by a licensed healthcare provider.
Mean weight loss in pivotal GLP-1 trials
| Medication | Trial (year) | Mean weight loss |
|---|---|---|
| Tirzepatide 15 mg | SURMOUNT-1 (2022) | 20.9% |
| Tirzepatide | SURMOUNT-5 (2025) | 20.2% |
| Semaglutide 2.4 mg | STEP 1 (2021) | 14.9% |
| Semaglutide 2.4 mg | SURMOUNT-5 (2025) | 13.7% |
| Oral semaglutide 25 mg | OASIS-4 (2025) | 13.6% |
| Oral orforglipron 36 mg | ATTAIN-1 (2025) | 12.4% |
Compounded versions are not the FDA-approved products studied in these trials.
Trials maximize titration, adherence, and support. In practice, side effects, cost, and gaps in follow-up lower average loss. Structured support narrows the gap — see how providers compare in our reviews.
Trials report roughly 15–21% on average over 68–72 weeks with support; individual real-world results vary and are often lower.
In head-to-head data (SURMOUNT-5, 2025), tirzepatide produced more average loss than semaglutide.