Mounjaro is licensed for type 2 diabetes, so its own trials are glycaemic trials in which weight was a secondary endpoint. Across the SURPASS programme, mean weight loss ran from 5.4 kg to 12.9 kg over 40 to 52 weeks in adults with type 2 diabetes, from the 5 mg arm of SURPASS-5 (PMID 35133415) to the 15 mg arm of SURPASS-3 (PMID 34370970).
The nearest percentage answer for the same molecule at the same doses is SURMOUNT-2, where adults with obesity and type 2 diabetes lost a mean of 14.7% of body weight over 72 weeks on 15 mg (PMID 37385275). Those two sets of numbers answer slightly different questions, and the difference between them is most of what makes this figure confusing.
- Mounjaro is tirzepatide licensed for type 2 diabetes. Every SURPASS trial used HbA1c as its primary endpoint and reported weight in kilograms as a secondary outcome.
- SURPASS-2: -7.6 kg, -9.3 kg and -11.2 kg on 5 mg, 10 mg and 15 mg over 40 weeks from a mean baseline of 93.7 kg, against -5.7 kg on semaglutide 1 mg.
- SURMOUNT-2 is the percentage trial: -12.8% on 10 mg and -14.7% on 15 mg over 72 weeks in 938 adults with obesity and type 2 diabetes, against -3.2% on placebo.
- The 20.9% figure circulating for tirzepatide is from SURMOUNT-1, which excluded people with diabetes. It is a Zepbound result, not a Mounjaro one.
Why the question has two legitimate answers
Tirzepatide is sold under two names at identical doses. Mounjaro is licensed for glycaemic control in type 2 diabetes. Zepbound is licensed for chronic weight management. The molecule, the six doses and the four-week escalation steps are the same, which is why the Mounjaro dosage chart and the Zepbound one describe the same ladder.
What differs is who was studied. The SURPASS trials enrolled adults with type 2 diabetes and measured HbA1c first. The SURMOUNT trials measured percentage weight change first, and SURMOUNT-1, the source of the famous numbers, specifically excluded diabetes. So for someone taking Mounjaro, both the diabetes trials and SURMOUNT-2 are relevant, and SURMOUNT-1 is not.
What the SURPASS trials measured in kilograms
Four phase 3 trials, each with a different comparator and background therapy, which is why the spread between trials is wider than the spread between doses.
| Trial | Design | Duration | Weight change at 5 / 10 / 15 mg | Comparator arm |
|---|---|---|---|---|
| SURPASS-1 (PMID 34186022) | Monotherapy vs placebo, 478 adults naive to injectables, BMI 31.9 | 40 weeks | -7.0 kg to -9.5 kg across the three doses | Placebo |
| SURPASS-2 (PMID 34170647) | Open-label vs semaglutide 1 mg on metformin, 1879 adults, mean 93.7 kg | 40 weeks | -7.6 / -9.3 / -11.2 kg | Semaglutide 1 mg -5.7 kg |
| SURPASS-3 (PMID 34370970) | Vs titrated insulin degludec, 1437 adults, mean 94.3 kg | 52 weeks | -7.5 kg to -12.9 kg across the three doses | Insulin degludec +2.3 kg |
| SURPASS-5 (PMID 35133415) | Added to titrated insulin glargine vs placebo, 475 adults | 40 weeks | -5.4 / -7.5 / -8.8 kg | Placebo +1.6 kg |
From the two trials that published a mean baseline weight, those kilogram figures work out at roughly 8% to 12% of starting weight in SURPASS-2 and 8% to 14% in SURPASS-3. Those are arithmetic from the reported means rather than percentages the trials reported, so they are not interchangeable with a primary endpoint like SURMOUNT-2’s.
The comparator columns carry real information. Against semaglutide 1 mg, which is an Ozempic dose rather than a Wegovy one, tirzepatide produced 1.9 kg, 3.6 kg and 5.5 kg more loss at the three doses. Against insulin degludec the gap is wider still, because the comparator arm gained 2.3 kg. The direct comparison between the two molecules in obesity is covered in semaglutide vs tirzepatide.
The percentage answer comes from SURMOUNT-2
SURMOUNT-2 randomised 938 adults with a BMI of 27 or above, type 2 diabetes and an HbA1c between 7% and 10% to tirzepatide 10 mg, 15 mg or placebo for 72 weeks. Mean baseline weight was 100.7 kg, mean BMI 36.1 and mean HbA1c 8.02%.
Mean weight change at week 72 was -12.8% on 10 mg and -14.7% on 15 mg, against -3.2% on placebo. Between 79% and 83% of participants on tirzepatide lost at least 5% of their starting weight, against 32% on placebo. This is the trial to reach for when the question is a percentage and the person asking has type 2 diabetes.
Note what it is not. SURMOUNT-2 ran for 72 weeks, not 40, and it enrolled people with obesity as well as diabetes. Its figures are not a longer version of SURPASS-2’s, they are a different trial with a different entry requirement and a weight endpoint.
Turn these percentages into pounds
Enter a starting weight and see what the SURPASS and SURMOUNT-2 figures work out to for you.
Type 2 diabetes is the biggest single modifier
The gap between the Mounjaro and Zepbound numbers is mostly the population, not the brand. The clearest demonstration is in the semaglutide programme, where the same dose was tested in both groups for the same length of time: STEP 1 recorded 14.9% over 68 weeks in adults without diabetes, and STEP 2 recorded 9.6% over the identical 68 weeks in adults with type 2 diabetes.
Real-world data follows the same pattern. In a cohort of 175 patients taking semaglutide for weight loss, six-month loss averaged 11.8% for those without type 2 diabetes and 7.2% for those with it. Tirzepatide shows the same direction: 20.9% in SURMOUNT-1 without diabetes against 14.7% in SURMOUNT-2 with it, at the same 15 mg dose over the same 72 weeks.
Why that happens is not fully settled. Candidate explanations include concurrent glucose-lowering drugs that promote weight gain, lower starting insulin sensitivity, and the fact that glycaemic trial populations are recruited on HbA1c rather than on BMI. Whatever the mechanism, roughly a third less weight loss is the consistent observation.
What none of these trials tells you
Weight was a secondary endpoint in every SURPASS trial, so those figures were not what the trials were powered to detect, and the background therapy differed in each one. None of the four published a month-by-month weight curve, and the first 20 weeks of any of these schedules is dose escalation rather than a maintenance dose.
They also say nothing about individuals. SURMOUNT-2 reported that 79% to 83% of participants reached 5% loss, which means a sixth to a fifth did not. If the question is what the weight-management programme for this molecule produced in people without diabetes, that is how much weight you can lose on Zepbound rather than this page.
FAQ
How much weight can you lose on Mounjaro in a year?
The closest figures come from trials of 40 to 52 weeks in adults with type 2 diabetes. SURPASS-2 recorded mean losses of 7.6 kg, 9.3 kg and 11.2 kg on tirzepatide 5 mg, 10 mg and 15 mg over 40 weeks from a mean baseline of 93.7 kg. SURPASS-3 recorded 7.5 kg to 12.9 kg over 52 weeks from a mean baseline of 94.3 kg.
What percentage of body weight does Mounjaro reduce?
Mounjaro’s own SURPASS trials reported weight in kilograms rather than as a headline percentage. The percentage figure for the same molecule and doses comes from SURMOUNT-2, where adults with obesity and type 2 diabetes lost a mean of 12.8% on 10 mg and 14.7% on 15 mg over 72 weeks, against 3.2% on placebo.
Is Mounjaro the same as Zepbound?
Both are tirzepatide at the same six doses from 2.5 mg to 15 mg. Mounjaro is licensed for type 2 diabetes and Zepbound for chronic weight management, which is why their trial programmes and headline numbers differ. The widely quoted 20.9% figure is from SURMOUNT-1, a 72-week obesity trial that excluded people with diabetes, so it belongs to Zepbound rather than Mounjaro.
Why do people with type 2 diabetes lose less weight?
It is a consistent pattern across both drug classes rather than something specific to tirzepatide. Semaglutide 2.4 mg produced 14.9% over 68 weeks in STEP 1 without diabetes and 9.6% over the same 68 weeks in STEP 2 with type 2 diabetes. A real-world semaglutide cohort showed the same split at six months, 11.8% without type 2 diabetes against 7.2% with it.
Does the 15 mg dose produce much more weight loss than 10 mg?
On weight, the step is consistent but modest. SURMOUNT-2 recorded 14.7% on 15 mg against 12.8% on 10 mg over 72 weeks, a difference of about two percentage points. SURPASS-2 showed 11.2 kg against 9.3 kg over 40 weeks. In SURPASS-5 the 15 mg arm had an 18% premature treatment discontinuation rate against 12% on 10 mg.
How fast does the weight come off on Mounjaro?
No SURPASS trial published a month-by-month curve, and the first 20 weeks are taken up by the four-week escalation steps rather than a maintenance dose. The nearest published early figures for this drug class come from a real-world semaglutide cohort, which averaged 5.9% at three months and 10.9% at six months across mixed doses.
Sources
- Rosenstock J, Wysham C, Frías JP, et al. Efficacy and safety of a novel dual GIP and GLP-1 receptor agonist tirzepatide in patients with type 2 diabetes (SURPASS-1). Lancet. 2021;398(10295):143-155. PMID: 34186022
- Frías JP, Davies MJ, Rosenstock J, et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes (SURPASS-2). N Engl J Med. 2021;385(6):503-515. PMID: 34170647
- Ludvik B, Giorgino F, Jódar E, et al. Once-weekly tirzepatide versus once-daily insulin degludec as add-on to metformin with or without SGLT2 inhibitors in patients with type 2 diabetes (SURPASS-3). Lancet. 2021;398(10300):583-598. PMID: 34370970
- Dahl D, Onishi Y, Norwood P, et al. Effect of Subcutaneous Tirzepatide vs Placebo Added to Titrated Insulin Glargine on Glycemic Control in Patients With Type 2 Diabetes: The SURPASS-5 Randomized Clinical Trial. JAMA. 2022;327(6):534-545. PMID: 35133415
- 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
- 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
- Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. PMID: 33567185
- Davies M, Féderèr Hansen K, Lingvay I, et al. Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2). Lancet. 2021;397(10278):971-984. PMID: 33667417
- Ghusn W, De la Rosa A, Sacoto D, et al. Weight Loss Outcomes Associated With Semaglutide Treatment for Patients With Overweight or Obesity. JAMA Netw Open. 2022;5(9):e2231982. PMID: 36121652
- MOUNJARO (tirzepatide) injection, US prescribing information, Eli Lilly and Company.
This article is for information only and is not medical advice. Dosing, suitability and any change to treatment are decisions for your prescriber.