In SURMOUNT-1, the trial behind Zepbound's approval, adults with obesity and no diabetes lost an average of 20.9% of body weight over 72 weeks on tirzepatide 15 mg, against 3.1% on placebo (PMID 35658024). From a mean starting weight of 104.8 kg, or about 231 lb, that is roughly 22 kg or 48 lb.
The dose changes that answer a great deal. The same trial recorded 19.5% on 10 mg and 15.0% on 5 mg, and a separate trial in people who also had type 2 diabetes came in several percentage points lower again. Here is what each Zepbound dose actually produced, in which population, and over how long.
- SURMOUNT-1 tested tirzepatide, the molecule in Zepbound, in 2539 adults with obesity and no diabetes: average loss over 72 weeks was 20.9% on 15 mg, 19.5% on 10 mg and 15.0% on 5 mg.
- SURMOUNT-2 ran the same doses for the same 72 weeks in adults who also had type 2 diabetes and recorded 14.7% on 15 mg and 12.8% on 10 mg.
- The 22.5% figure quoted elsewhere is the same SURMOUNT-1 15 mg arm counted a different way, under the efficacy estimand rather than the treatment-regimen estimand.
- Continuing past 72 weeks kept working: the SURMOUNT-1 prediabetes group was 19.7% below baseline at 176 weeks on 15 mg.
What Zepbound is, and which trials carry its numbers
Zepbound is tirzepatide, a once-weekly injection that activates both the GIP and GLP-1 receptors. The US Food and Drug Administration approved it in November 2023 for chronic weight management in adults with obesity, or with overweight plus at least one weight-related condition, and added an indication for moderate to severe obstructive sleep apnea in adults with obesity in December 2024.
The same molecule is sold as Mounjaro for type 2 diabetes. That matters for reading percentages, because the two brands share a dose range and a molecule but not a trial programme. Zepbound's weight figures come from the SURMOUNT trials; Mounjaro's come from SURPASS, which measured blood glucose first and weight second.
The label runs 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg and 15 mg once weekly. The 2.5 mg strength is for starting only and is not a maintenance dose, and the licensed maintenance doses are 5 mg, 10 mg and 15 mg. SURMOUNT-1 tested exactly those three maintenance doses, which is why the trial table below has three rows rather than one.
How much weight can you lose on Zepbound?
Every figure below names its trial, its dose, whether participants had type 2 diabetes, and how long it ran. A percentage missing any of those four is not comparable to the others.
| Trial | Dose | Population | Duration | Mean weight change |
|---|---|---|---|---|
| SURMOUNT-1 (PMID 35658024) | Tirzepatide 15 mg | Obesity, no diabetes | 72 weeks | -20.9% (placebo -3.1%) |
| SURMOUNT-1 (PMID 35658024) | Tirzepatide 10 mg | Obesity, no diabetes | 72 weeks | -19.5% |
| SURMOUNT-1 (PMID 35658024) | Tirzepatide 5 mg | Obesity, no diabetes | 72 weeks | -15.0% |
| SURMOUNT-2 (PMID 37385275) | Tirzepatide 15 mg | Obesity with type 2 diabetes | 72 weeks | -14.7% (placebo -3.2%) |
| SURMOUNT-2 (PMID 37385275) | Tirzepatide 10 mg | Obesity with type 2 diabetes | 72 weeks | -12.8% |
| SURMOUNT-1 at 176 weeks (PMID 39536238) | Tirzepatide 15 mg | Obesity and prediabetes | 176 weeks | -19.7% (placebo -1.3%) |
Dose by dose, without type 2 diabetes
SURMOUNT-1 randomly assigned 2539 adults with a BMI of 30 or above, or 27 and above with a weight-related complication, to tirzepatide 5 mg, 10 mg, 15 mg or placebo for 72 weeks, with a 20-week dose escalation at the start. Diabetes was an exclusion. Mean BMI at baseline was 38.0.
The spread across the three doses was 15.0%, 19.5% and 20.9%. Notice where the gap sits: going from 5 mg to 10 mg was worth about 4.5 percentage points, while going from 10 mg to 15 mg added closer to 1.4. The curve steepens early in the dose range and flattens at the top of it.
Thresholds are more useful than averages. At week 72, 85% of the 5 mg group, 89% of the 10 mg group and 91% of the 15 mg group had lost at least 5% of their starting weight, against 35% on placebo. For a 20% loss, the figures were 50% on 10 mg and 57% on 15 mg, against 3% on placebo. So more than half the people on the top dose halved the distance to a fifth of their body weight, and a substantial minority did not.
With type 2 diabetes: several points lower
SURMOUNT-2 ran 72 weeks in 938 adults with obesity and type 2 diabetes, with an HbA1c between 7% and 10%, comparing tirzepatide 10 mg, 15 mg and placebo. Mean baseline weight was 100.7 kg. Weight change was -12.8% on 10 mg and -14.7% on 15 mg, against -3.2% on placebo, and 79% to 83% of those on tirzepatide lost at least 5% against 32% on placebo.
Same molecule, same doses, same 72 weeks, about six percentage points less. That gap between populations with and without type 2 diabetes shows up across this drug class. It appears in the semaglutide data too, which we covered in the piece on how much weight you can lose on Wegovy.
Why you also see 22.5% quoted
Both 20.9% and 22.5% describe the 15 mg arm of SURMOUNT-1. They differ because the trial reported two estimands, which are two different questions asked of the same data.
The treatment-regimen estimand, which produced 20.9%, counts everyone randomly assigned to the dose, including participants who stopped the drug part way through and were weighed anyway. It answers what happened to people started on this dose. The efficacy estimand, which produced 22.5%, estimates what would have happened had everyone stayed on treatment throughout. It answers what the drug does when taken as intended.
Neither number is wrong, and the roughly 1.6 point gap between them is mostly discontinuation. Adverse events ended treatment for 6.2% of the 15 mg group, 7.1% of the 10 mg group and 4.3% of the 5 mg group, against 2.6% on placebo. The problem is only comparison: setting the 22.5% efficacy figure against a treatment-regimen percentage from another trial makes tirzepatide look better than a like-for-like reading supports. The table above uses treatment-regimen figures throughout.
What the first year actually looks like
SURMOUNT-1 reports its endpoint, not a monthly curve, and the 20-week escalation means nobody reached 15 mg before about month five. For an earlier picture the best available source is real-world dispensing data.
A cohort study of 18,386 propensity-matched US adults with overweight or obesity tracked on-treatment weight change on tirzepatide in the diabetes-labelled formulation, which runs the same 2.5 mg to 15 mg range. About 52% had type 2 diabetes and mean baseline weight was 110 kg.
| Point in treatment | Average loss | Where it comes from |
|---|---|---|
| 3 months | 5.9% | Real-world cohort, tirzepatide, mixed doses, about half with type 2 diabetes |
| 6 months | 10.1% | Same cohort |
| 12 months | 15.3% | Same cohort |
| Week 72, about 16.5 months | 20.9% | SURMOUNT-1, tirzepatide 15 mg, no diabetes |
| Week 176, about 3.4 years | 19.7% | SURMOUNT-1 prediabetes group, tirzepatide 15 mg |
Two caveats on that table. The cohort was prescribed a range of doses rather than 15 mg across the board and around half had type 2 diabetes, so its figures sit below what a trial of the top dose in people without diabetes records. And the first three rows are on-treatment measurements, meaning they describe people still taking the drug at that point, which is a different denominator from a trial average.
Three years in, the curve is flat rather than falling
SURMOUNT-1 continued to 176 weeks in the 1032 participants who had both obesity and prediabetes at enrolment. Mean weight change at week 176 was -19.7% on 15 mg, -18.7% on 10 mg and -12.3% on 5 mg, against -1.3% on placebo.
Those numbers sit slightly below the 72-week figures for the full cohort, but they are a different subgroup measured more than two years later, so the comparison is loose. What both readings show is the same shape: a steep first year while the dose escalates, then a long plateau. The trial also recorded type 2 diabetes in 1.3% of the tirzepatide groups over those 176 weeks against 13.3% on placebo.
See what 20.9% looks like from your starting weight
Turn the SURMOUNT-1 percentages into pounds and a week-by-week curve for your own numbers.
A percentage is easy to quote and hard to picture. Running your own starting weight through a GLP-1 weight loss calculator turns 20.9% into a pound figure and a week-by-week shape, which is a steadier reference point than a population average. If you want to see how different tools handle this, we compared the main online weight loss calculators and the data each is built on.
What the data shows about stopping
SURMOUNT-4 was built to answer this directly. It gave 670 adults with obesity or overweight 36 weeks of open-label tirzepatide at their maximum tolerated dose of 10 mg or 15 mg, producing a mean loss of 20.9%, then randomly assigned them to continue or switch to placebo for another 52 weeks.
From week 36 to week 88, those who continued lost a further 5.5%. Those switched to placebo gained 14.0%. By week 88, 89.5% of the continuing group had held on to at least 80% of what they lost during the lead-in, against 16.6% of the placebo group. Total change from the start of the trial was -25.3% with continued treatment and -9.9% after withdrawal.
That is the clearest statement in the tirzepatide literature that the weight comes back when treatment stops, which is why prescribers generally frame it as ongoing rather than a fixed course.
How it compares with semaglutide
SURMOUNT-5 is the only direct head-to-head. It was an open-label trial in 751 adults with obesity and no type 2 diabetes, comparing maximum tolerated tirzepatide, meaning 10 mg or 15 mg, against maximum tolerated semaglutide, meaning 1.7 mg or 2.4 mg, over 72 weeks. Weight change was -20.2% on tirzepatide and -13.7% on semaglutide, and waist circumference fell 18.4 cm against 13.0 cm.
That is a real comparison, unlike lining up SURMOUNT-1 against a semaglutide trial run in a different population under different rules. Worth noting: the semaglutide 2.4 mg dose in that trial is a Wegovy dose, not one Ozempic can reach, since Ozempic's maximum is 2 mg.
Why individual results vary this much
Within the SURMOUNT-1 15 mg group, 57% lost at least 20% of their body weight while 9% did not reach 5%, on the same dose for the same 72 weeks. The factors behind that spread are well documented:
- Dose reached. The gap between 5 mg and 15 mg was about six percentage points in SURMOUNT-1. Trial averages assume people reached and stayed on their assigned dose.
- Type 2 diabetes status. The largest single split in the data, worth roughly six points at 72 weeks between SURMOUNT-1 and SURMOUNT-2.
- Time on treatment. The curve is front-loaded and the escalation runs 20 weeks, so someone four months in and someone 16 months in are not comparable.
- Starting weight. The same percentage means very different pound counts from 300 lb and from 180 lb.
- The lifestyle intervention. Every SURMOUNT trial paired the drug with reduced-calorie diet and activity counselling in both arms, placebo included.
FAQ
How much weight can you lose on Zepbound in a year?
The nearest trial figure is SURMOUNT-1, which ran 72 weeks, slightly under 17 months. Adults with obesity and no diabetes lost an average of 20.9% of body weight on tirzepatide 15 mg, 19.5% on 10 mg and 15.0% on 5 mg. A real-world cohort of adults taking tirzepatide in the diabetes-labelled formulation recorded 15.3% at 12 months on treatment, which is the closer comparison for a calendar year.
Is Zepbound the same as Mounjaro?
Both are tirzepatide and both run from 2.5 mg to 15 mg once weekly. Mounjaro is licensed for type 2 diabetes and Zepbound for chronic weight management and for moderate to severe obstructive sleep apnea in adults with obesity. The weight loss trials behind Zepbound are the SURMOUNT programme, and the diabetes trials behind Mounjaro are the SURPASS programme.
Why do some sites say Zepbound produces 22.5% weight loss?
Both numbers come from the same 15 mg arm of SURMOUNT-1. The 20.9% figure is the treatment-regimen estimand, which counts everyone randomly assigned to the dose including people who stopped early. The 22.5% figure is the efficacy estimand, which estimates what would have happened if everyone had stayed on treatment. Neither is wrong, but they answer different questions and should not be compared against a percentage calculated the other way.
How much weight can you lose on Zepbound with type 2 diabetes?
In SURMOUNT-2, 938 adults with obesity and type 2 diabetes took tirzepatide 10 mg, 15 mg or placebo for 72 weeks. Average weight change was 12.8% on 10 mg, 14.7% on 15 mg and 3.2% on placebo. That is roughly six percentage points less than SURMOUNT-1 recorded at the same doses and duration in people without diabetes.
Does Zepbound stop working after a while?
In SURMOUNT-1 the 176-week analysis of participants with obesity and prediabetes recorded 19.7% on 15 mg and 18.7% on 10 mg, against 20.9% and 19.5% for the full cohort at 72 weeks. The curve flattens well before three years rather than reversing, so most of the loss in those trials landed inside the first 18 months.
What happens if you stop taking Zepbound?
SURMOUNT-4 gave 670 adults 36 weeks of open-label tirzepatide, by which point they had lost an average of 20.9%, then randomly assigned them to continue or switch to placebo for 52 weeks. Those who continued lost a further 5.5%. Those switched to placebo gained 14.0% back over the same period.
Sources
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. PMID: 35658024
- Garvey WT, Frias JP, Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity in people with type 2 diabetes (SURMOUNT-2): a double-blind, randomised, multicentre, placebo-controlled, phase 3 trial. Lancet. 2023;402(10402):613-626. PMID: 37385275
- Aronne LJ, Sattar N, Horn DB, et al. Continued Treatment With Tirzepatide for Maintenance of Weight Reduction in Adults With Obesity: The SURMOUNT-4 Randomized Clinical Trial. JAMA. 2024;331(1):38-48. PMID: 38078870
- Jastreboff AM, le Roux CW, Stefanski A, et al. Tirzepatide for Obesity Treatment and Diabetes Prevention. N Engl J Med. 2025;392(10):958-971. PMID: 39536238
- Aronne LJ, Horn DB, le Roux CW, et al. Tirzepatide as Compared with Semaglutide for the Treatment of Obesity (SURMOUNT-5). N Engl J Med. 2025;393(1):26-36. PMID: 40353578
- Rodriguez PJ, Goodwin Cartwright BM, Gratzl S, et al. Semaglutide vs Tirzepatide for Weight Loss in Adults With Overweight or Obesity. JAMA Intern Med. 2024;184(9):1056-1064. PMID: 38976257
- US Food and Drug Administration. Zepbound (tirzepatide) injection prescribing information. Approved November 2023; obstructive sleep apnea indication added December 2024.
This article is for information only and is not medical advice. Dosing, suitability and any change to treatment are decisions for your prescriber.