Tirzepatide vs semaglutide: how much weight could you lose?
In the only head-to-head randomized trial of the two leading weight-loss medications, people taking tirzepatide lost 20.2% of their body weight on average over 72 weeks, compared with 13.7% with semaglutide — the SURMOUNT-5 trial, published in the peer-reviewed New England Journal of Medicine in 2025. Enter your starting weight below to see what those trial averages would mean at your size.
Data verified September 2, 2026 against the published trial and its ClinicalTrials.gov results record.
Based on SURMOUNT-5, a peer-reviewed head-to-head clinical trial published in the New England Journal of Medicine (2025).
The shaded bands show the range around the study average (the 95% confidence interval). Only the week-72 numbers were measured in the study — the curve in between is an estimate of the path, not measured data.
How you compare to who was studied
- Your BMI is about 33.5. That is within the trial’s inclusion range (BMI ≥30), so the study population resembles you on this measure.
Want to know what’s realistic for you?
These curves show study averages — not your number. A licensed provider can look at your health and tell you what to expect, and which medication fits you.
Which works better for weight loss: tirzepatide or semaglutide?
Tirzepatide produced significantly more weight loss than semaglutide in the direct comparison. SURMOUNT-5 randomized 751 adults with obesity (and without type 2 diabetes) to the maximum tolerated dose of one drug or the other for 72 weeks. The average difference was about 6.5 percentage points of body weight — roughly 47% more relative weight loss with tirzepatide. Every efficacy measure the trial reported favored tirzepatide: average weight change, every weight-loss threshold from 10% to 30%, waist circumference, and BMI change.
| SURMOUNT-5 result (72 weeks) | Tirzepatide | Semaglutide |
|---|---|---|
| Average weight change at 72 weeks | -20.2% | -13.7% |
| 95% confidence interval | -21.4% to -19.1% | -14.9% to -12.6% |
| Lost ≥10% of body weight | 81.6% | 60.5% |
| Lost ≥15% of body weight | 64.6% | 40.1% |
| Lost ≥20% of body weight | 48.4% | 27.3% |
| Lost ≥25% of body weight | 31.6% | 16.1% |
| Waist circumference change | -18.4 cm | -13 cm |
| BMI change | -8.5 kg/m² | -6 kg/m² |
| Dose studied | 10 or 15 mg weekly (maximum tolerated dose) | 1.7 or 2.4 mg weekly (maximum tolerated dose) |
“Among participants with obesity but without diabetes, treatment with tirzepatide was superior to treatment with semaglutide with respect to reduction in body weight and waist circumference at week 72.”
Continue reading
What are your chances of losing 15% or more?
Averages hide the spread, so the threshold numbers matter more than the headline. On tirzepatide, 64.6% of participants lost at least 15% of their body weight and 31.6% lost at least a quarter of it. On semaglutide, 40.1% reached 15% and 16.1% reached 25%. At the other end, 18.4% of tirzepatide and 39.5% of semaglutide participants lost less than 10% — a real outcome on either drug.
How do the side effects compare?
Both medications had mostly gastrointestinal side effects, typically mild to moderate and concentrated during dose escalation. Rates were broadly similar; vomiting was somewhat more common with semaglutide. Nausea, the most common of them, is usually manageable with practical adjustments.
| Side effect (% of participants) | Tirzepatide | Semaglutide |
|---|---|---|
| Nausea | 43.6% | 44.4% |
| Constipation | 27% | 28.5% |
| Diarrhea | 23.5% | 23.4% |
| Vomiting | 15% | 21.3% |
Who was studied?
Phase 3b, open-label, randomized controlled trial. Adults with obesity (BMI ≥30, or ≥27 with a weight-related comorbidity) and without type 2 diabetes received the maximum tolerated dose of tirzepatide (10 or 15 mg) or semaglutide (1.7 or 2.4 mg) once weekly for 72 weeks. Participants averaged 44.7 years old, and 64.7% were female. People with diabetes were excluded, so these numbers do not describe results for people with type 2 diabetes.
How this simulator works
The tool multiplies your starting weight by the trial’s average percent weight change (-20.2% for tirzepatide, -13.7% for semaglutide). The shaded bands show the 95% confidence intervals — a statistical range of uncertainty around each trial average. Only the 72-week endpoints are measured trial data; the curve connecting week 0 to week 72 is an estimate shaped like the fast-early-loss-then-leveling-off pattern these medications consistently show in trials — here’s how long it typically takes to see weight loss on a GLP-1. Nothing you enter is stored or sent anywhere — the simulation runs entirely in your browser.
Sources
- Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity. N Engl J Med 2025;393(1):26-36. Published in the New England Journal of Medicine, a peer-reviewed medical journal. DOI: 10.1056/NEJMoa2416394
- Posted trial results, ClinicalTrials.gov NCT05822830 (BMI change, baseline characteristics, adverse events).
Frequently asked questions
Which is more effective for weight loss, tirzepatide or semaglutide?+−
Tirzepatide. In SURMOUNT-5, the only head-to-head randomized trial, participants on tirzepatide lost 20.2% of body weight on average at 72 weeks versus 13.7% with semaglutide.
How much weight could I lose on tirzepatide?+−
Trial participants on tirzepatide (10 or 15 mg weekly) averaged 20.2% body-weight loss over 72 weeks. 48.4% lost at least 20% of their body weight, and 81.6% lost at least 10%. Individual results vary widely.
How much weight could I lose on semaglutide?+−
Trial participants on semaglutide (1.7 or 2.4 mg weekly) averaged 13.7% body-weight loss over 72 weeks. 27.3% lost at least 20% of their body weight, and 60.5% lost at least 10%. Individual results vary widely.
Is this simulator a prediction of my results?+−
No. It applies the average results of one clinical trial to your starting weight. Individual outcomes range from little change to far more than the average. Only a licensed clinician can assess what is realistic for you.
Do tirzepatide and semaglutide have different side effects?+−
Both are mainly associated with gastrointestinal side effects, mostly mild to moderate and concentrated during dose escalation. In the head-to-head trial, nausea affected 43.6% (tirzepatide) vs 44.4% (semaglutide), and vomiting 15% vs 21.3%.
Why does tirzepatide cause more weight loss than semaglutide?+−
Tirzepatide activates two gut-hormone receptors, GIP and GLP-1, while semaglutide activates GLP-1 alone. Researchers attribute the larger average weight loss to this dual action, though the exact mechanism is still being studied.
Can you switch from semaglutide to tirzepatide?+−
Yes — but it is a decision to make with your clinician, and there is no accepted formula for converting doses between the two drugs. SURMOUNT-5 compared them separately and did not study switching, so its results do not predict what happens after a switch.
Which costs more, tirzepatide or semaglutide?+−
U.S. list prices for the branded versions are broadly similar. A published cost-effectiveness analysis based on SURMOUNT-5 — a modeling study authored in part by researchers at tirzepatide’s manufacturer — projected tirzepatide to be less costly and more effective over the long term. Actual out-of-pocket cost depends on insurance coverage and pharmacy.
How quickly does weight loss start on these medications?+−
In trials of both drugs, weight loss typically begins within the first month and is fastest in the early months before gradually leveling off. Only the 72-week endpoint in this tool is measured trial data.
What happens if you stop taking tirzepatide or semaglutide?+−
Studies of GLP-1 medications consistently show that much of the lost weight returns after stopping treatment. SURMOUNT-5 did not study what happens after discontinuation — decisions about staying on treatment belong with your clinician.
Did SURMOUNT-5 test the highest dose of semaglutide?+−
It compared the maximum approved doses at the time: tirzepatide 10 or 15 mg versus semaglutide 1.7 or 2.4 mg. A higher 7.2 mg semaglutide dose was approved after the trial ran and has not been compared head-to-head with tirzepatide, so this page reflects the doses actually tested against each other.
This page is for educational purposes only and is not medical advice, diagnosis, or treatment. All results shown come from a single clinical trial (SURMOUNT-5) and describe group averages, not individual predictions. Talk with a licensed clinician before starting, stopping, or switching any medication.