Zepbound's trials recorded an average weight loss of about 15% to 21% over 72 weeks, depending on the dose, against about 3% on placebo. The figure moves with who was studied: lower in people with type 2 diabetes, higher when a diet programme came first, and reversed when the drug was stopped. This page lays out every trial in the SURMOUNT programme and what each one measured.
The trial numbers come from the Zepbound prescribing information (effective 28 August 2026) and the published trial reports, read on 15 October 2026. The conversions into kilograms are glp1ledger's arithmetic, labelled where they appear. What Zepbound is and how it is sold are on what is Zepbound; this page is the results.
Every trial, in one table
| Trial | Who | Length | Zepbound | Placebo or comparator |
|---|---|---|---|---|
| SURMOUNT-1 (Study 1) | 2,539 adults with obesity or overweight, no diabetes | 72 weeks | -15.0% (5 mg) · -19.5% (10 mg) · -20.9% (15 mg) | -3.1% |
| SURMOUNT-2 (Study 2) | 938 adults with type 2 diabetes | 72 weeks | -12.8% (10 mg) · -14.7% (15 mg) | -3.2% |
| SURMOUNT-3 (Study 3) | 579 adults who first lost ≥5% on a 12-week intensive diet programme | 72 weeks after the diet phase | -18.4% further | +2.5% |
| SURMOUNT-4 (Study 4) | 670 adults who had already taken Zepbound for 36 weeks | 52 weeks after randomisation | -5.5% further | +14.0% (switched to placebo) |
| SURMOUNT-OSA (Studies 5 and 6) | 469 adults with obesity and moderate-to-severe sleep apnoea | 52 weeks | -17.7% · -19.6% | -1.6% · -2.3% |
| SURMOUNT-5 | 751 adults with obesity, no diabetes | 72 weeks | -20.2% | -13.7% on semaglutide |
| SURMOUNT-1, three-year extension | Participants with prediabetes | 176 weeks | -12.3% (5 mg) · -18.7% (10 mg) · -19.7% (15 mg) | -1.3% |
Least-squares mean percent change from baseline. SURMOUNT-1 to -4 and the sleep apnoea trials: Zepbound label, section 14 (Studies 1–6). SURMOUNT-5 and the three-year extension: New England Journal of Medicine, 2025.
What the percentages mean in kilograms
The label reports percentages. glp1ledger converted them using each arm's own baseline weight from the same table (ratio of the reported means, so approximate):
| SURMOUNT-1 arm | Baseline weight | Mean change | About |
|---|---|---|---|
| Placebo | 104.8 kg | -3.1% | 3 kg |
| 5 mg | 102.9 kg | -15.0% | 15 kg |
| 10 mg | 105.8 kg | -19.5% | 21 kg |
| 15 mg | 105.6 kg | -20.9% | 22 kg |
For someone weighing less than the trial average, the same percentage is fewer kilograms; heavier, more. A percentage is the more transportable figure.
The spread behind the average
An average of about 21% does not mean most people lost about 21%. The label reports how many people crossed each threshold in SURMOUNT-1:
| Lost at least | Placebo | 5 mg | 10 mg | 15 mg |
|---|---|---|---|---|
| 5% | 34.5% | 85.1% | 88.9% | 90.9% |
| 10% | 18.8% | 68.5% | 78.1% | 83.5% |
| 15% | 8.8% | 48.0% | 66.6% | 70.6% |
| 20% | 3.1% | 30.0% | 50.1% | 56.7% |
Read from the other end: on the highest dose, roughly one person in eleven did not reach a 5% loss and more than four in ten did not reach 20%. The trials did not identify in advance who would respond strongly; the label gives the distribution, not a predictor.
In SURMOUNT-2, in type 2 diabetes, 30.8% on 15 mg reached a 20% loss, against 56.7% in SURMOUNT-1. The gap between people with and without diabetes appears across the whole GLP-1 class; Mounjaro vs Zepbound works through it for tirzepatide. SURMOUNT-1 also kept its participants with prediabetes on treatment for 176 weeks, and how many of them developed diabetes is set out on GLP-1 drugs for prediabetes.
Three trials that answer different questions
SURMOUNT-3 asked what Zepbound adds after a diet has already worked. Everyone first spent 12 weeks on an intensive programme with a dietitian; only those who lost at least 5% went on, and they had lost 6.9% on average. Over the next 72 weeks, the Zepbound group lost a further 18.4% while the placebo group regained 2.5% — a gap of 20.8 points, the widest placebo difference in the programme. Waist circumference fell 14.6 cm on Zepbound against a 0.2 cm rise on placebo.
SURMOUNT-4 asked what happens when the drug stops. All 783 enrolled adults took open-label Zepbound for 36 weeks; 670 were then randomised to continue or switch to placebo. The label gives the group's average weight as 107.3 kg at the start and 84.6–85.8 kg at week 36 — by glp1ledger's arithmetic, a fall of about a fifth in 36 weeks. Over the next 52 weeks the continuing group lost a further 5.5% while the switched group regained 14.0%. Applying those percentages to the week-36 averages, the continuing group finished around 80 kg and the switched group around 98 kg — still below where they started, but most of the way back. What else changed on stopping is on stopping GLP-1 drugs.
The three-year extension of SURMOUNT-1 asked whether the loss holds and what it does to diabetes risk. In participants who had prediabetes at the start, the 176-week change was -19.7% on 15 mg against -1.3% on placebo, and 1.3% of those on tirzepatide developed type 2 diabetes against 13.3% on placebo. After 17 weeks off treatment, those figures were 2.4% and 13.7%.
Sleep apnoea: weight as a secondary result
The two SURMOUNT-OSA trials were run for Zepbound's sleep apnoea indication, so their primary measure was breathing interruptions per hour (the apnoea-hypopnoea index), not weight. Weight was recorded anyway: -17.7% and -19.6% at 52 weeks against -1.6% and -2.3% on placebo, at the maximum tolerated dose of 10 or 15 mg. The breathing results and what the indication covers are on GLP-1 and sleep apnea.
What these results do not tell you
- Results outside a trial. Trial participants had regular visits, dietary counselling and a set dose schedule; missing data were imputed by the methods the label describes. Clinic and pharmacy records from routine use are a different kind of evidence.
- Who will respond. The tables show the spread, not which person lands where.
- Body composition. The label reports weight and waist, not how much of the loss was muscle; that question is on our muscle loss page, and the drugs being tested to protect muscle are on bimagrumab.
- Beyond three years. The longest published Zepbound follow-up is 176 weeks.
The doses in the tables are the doses the trials tested, reported as results. Which medicine and which dose suit a particular person, if any, is a decision for that person and their prescriber. The side effects recorded in the same trials are on Zepbound side effects.
Sources
- Eli Lilly and Company, ZEPBOUND (tirzepatide) prescribing information, effective 2026-08-28 (version 40), section 14, Tables 2, 4, 6 and 9 (Studies 1–6: SURMOUNT-1, -2, -3, -4 and SURMOUNT-OSA), via openFDA (set id 487cd7e7-434c-4925-99fa-aa80b1cc776b), read 2026-10-15.
- Aronne LJ et al. "Tirzepatide as compared with semaglutide for the treatment of obesity." N Engl J Med 2025 (SURMOUNT-5), PubMed 40353578.
- Jastreboff AM et al. "Tirzepatide for obesity treatment and diabetes prevention." N Engl J Med 2025 (SURMOUNT-1 three-year results), PubMed 39536238.
- ClinicalTrials.gov records NCT04657016 (SURMOUNT-3) and NCT04660643 (SURMOUNT-4) as cited in the label.