Mounjaro weight loss percentage: what the evidence says

What SURMOUNT-1 actually measured

SURMOUNT-1 ran for 72 weeks and randomised 2,539 adults with a BMI of 30 or above, or 27 or above alongside at least one weight-related condition. Participants received tirzepatide at 5mg, 10mg or 15mg, or a placebo, alongside a reduced-calorie diet and increased physical activity. The headline Mounjaro weight loss percentage figures were 15.0%, 19.5% and 20.9% at those three doses respectively, each meaningfully larger than the 3.1% seen in the placebo group. At 15mg, some analyses placed the average closer to 22.5%. NICE's appraisal of tirzepatide (TA1026) drew directly on this data when recommending Mounjaro for NHS use in December 2024. Participants who lost less than 5% of their body weight after six months at the highest tolerated dose were identified as unlikely to benefit substantially, a threshold NICE built into its stopping guidance. If you want to see how those figures break down across the full range of tirzepatide weight loss percentage trials, including what each phase of the SURMOUNT programme measured and under what conditions, that data is set out in detail on this site. The trial was not designed to predict what any individual will lose; it measured what happened across thousands of participants under controlled conditions.

The head-to-head result: tirzepatide versus semaglutide

For years the tirzepatide weight loss percentage was compared only indirectly with semaglutide, which is the active ingredient in Wegovy. The SURMOUNT-5 trial, published in the New England Journal of Medicine in 2025, settled that question more directly. Over 72 weeks in 751 adults with obesity and no diabetes, tirzepatide produced greater average weight reduction than semaglutide 2.4mg. NICE's committee discussion notes that indirect comparisons had already favoured tirzepatide; SURMOUNT-5 gave those comparisons firmer ground. It is worth being clear about one common misconception here: many people assume Wegovy and Mounjaro produce essentially the same result because they act on overlapping pathways. They do not, tirzepatide activates both GIP and GLP-1 receptors, while semaglutide targets GLP-1 alone, and that dual action appears to account for the difference in average outcomes. For a detailed look at how the SURMOUNT programme data stacks up across doses and populations, the SURMOUNT trials breakdown on this site goes further. Which medicine suits you, however, is a clinical question.

What affects the percentage a person actually sees?

Trial averages are means across a large, heterogeneous group. Individual Mounjaro weight loss percentage results depend on several things that vary person to person. Dose matters: the 5mg figure is roughly three-quarters of the 15mg figure, and most people start at 2.5mg (a dose chosen to help your system adjust, not to produce weight loss) before titrating upward. Duration matters too; most of the weight change in SURMOUNT-1 occurred in the first 36 weeks, with further progress continuing more slowly to 72 weeks. Diet and activity are not optional extras: participants in the trial followed a structured deficit diet alongside the medicine, and the week-by-week pattern of weight change reflects that combination, not the injection alone. Individual biology, gut tolerance, starting weight and any concurrent conditions all influence the final number. For a broader look at what else shapes outcomes on this treatment, the Mounjaro weight loss overview covers the full picture. If you want to understand what a realistic trajectory might look like for your situation, that conversation starts with a prescriber, not with a trial table.

Safety context and how to access treatment

The tirzepatide weight loss percentage data is striking, but the trial populations also help define who the medicine is licensed for. In the UK, Mounjaro is licensed for adults with a BMI of 30 or above, or 27 or above with at least one weight-related condition such as high blood pressure, type 2 diabetes or obstructive sleep apnoea, and the SURMOUNT-OSA tirzepatide weight loss percentage findings are particularly relevant for people in that last category. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. The medicine carries a Black Triangle designation, meaning the MHRA collects additional safety data; anyone experiencing suspected side effects can report them via the Yellow Card scheme. NICE recommends tirzepatide within the NHS for adults with a BMI of 35 or above and at least one weight-related comorbidity, but private routes are available for people who do not meet those thresholds or prefer not to wait. You can read more about the clinical profile of tirzepatide or explore weight-loss treatment options if you are weighing up which approach fits your circumstances. Our clinical team reviews every consultation personally, and any repeat prescription is re-assessed before dispatch.