Tirzepatide weight loss percentages from the clinical trials

Where the 20% figure comes from, and what the trial actually measured

The most-cited result from the tirzepatide trials is the approximately 20–21% average body-weight reduction seen at the 15 mg dose in SURMOUNT-1. That trial randomised 2,539 adults who had obesity, or overweight with at least one weight-related condition such as high blood pressure or dyslipidaemia, but who did not have type 2 diabetes. Participants received either tirzepatide (at 5 mg, 10 mg or 15 mg) or placebo alongside a reduced-calorie diet and increased activity, for 72 weeks. The results, published in the New England Journal of Medicine, showed that the percentage of weight lost rose steadily with dose: the 5 mg group averaged around 15%, the 10 mg group around 19.5%, and the 15 mg group around 20–21%. Some analyses of the 15 mg data, accounting for participants who discontinued, reached approximately 22.5%. These are averages across a large group, individual results varied above and below, which is why the figures are always reported with a range and a confidence interval, not as a single promised number. NICE's appraisal of tirzepatide (TA1026) drew directly on this evidence when making its recommendation.

How dose escalation shapes those percentages, and why the starting dose is different from the therapeutic one

Tirzepatide treatment begins at 2.5 mg, a dose chosen to allow the body to adjust gradually and reduce early gastrointestinal side effects rather than to produce meaningful weight loss from week one. From there, the prescriber typically steps the dose upward in 4-week intervals through 5 mg, 7.5 mg, 10 mg, 12.5 mg and, if tolerated, 15 mg. The SURMOUNT-1 percentages listed above are the results at maintained therapeutic doses, not at the starting point. It is worth understanding that distinction before interpreting any trial figure: the 20% result is the outcome of 72 weeks at a sustained dose, not what a patient should expect at month one. The SURMOUNT trial breakdown on this site goes deeper into what the individual dose-arm data looked like across the full programme. If you are deciding which dose is right for you, that is a clinical conversation, not one to resolve from a percentage chart, a prescriber weighs your individual picture.

SURMOUNT-5: what the head-to-head comparison with semaglutide showed

For much of the last few years the GLP-1 trials ran in parallel rather than against each other, making direct comparisons difficult. SURMOUNT-5, published in the New England Journal of Medicine in 2025, changed that. It randomised 751 adults with obesity and no diabetes to either tirzepatide or semaglutide 2.4 mg, the standard weekly injection dose of Wegovy, over 72 weeks. Tirzepatide produced greater average weight reduction. NICE's committee, in its TA1026 discussion notes, acknowledged that indirect comparisons consistently favoured tirzepatide over semaglutide at that dose. The arrival of the higher 7.2 mg semaglutide dose narrows the gap somewhat (trial data at 7.2 mg reported around 20.7% average weight loss) so the picture continues to evolve. If you want a detailed look at what Mounjaro weight loss percentages look like across the trial programme, including how the dose arms compare, that page sets out the numbers clearly. For a fuller look at how the two medicines compare across multiple measures, the Mounjaro weight loss trials page covers the evidence in context. If cost is part of your thinking, the Mounjaro pricing page sets out what private treatment typically involves.

What these percentages mean for anyone considering treatment

A 20% reduction in body weight is clinically significant, reducing risk across blood pressure, blood sugar, cholesterol and sleep. Even the lower end of the trial range, around 15% at 5 mg, is well above what most people achieve through diet and activity alone over the same period, according to NICE's appraisal (TA1026). That said, trial conditions differ from real life. Participants had regular contact with study teams, consistent lifestyle support and no gaps in supply. The question is not simply whether the percentage is impressive in a trial, but whether someone is clinically suitable, willing to engage with the lifestyle component, and properly monitored throughout. NICE recommends reviewing whether to continue if less than 5% weight loss has occurred after six months at the highest tolerated dose. Many people find the first few weeks the hardest, particularly around nausea after a dose step. Research into the SURMOUNT-OSA tirzepatide weight loss percentage is also worth reviewing, as that trial examined outcomes in people with obesity-related sleep apnoea and adds useful context about how results can differ across different patient populations. Knowing that ahead of time, and having a prescriber to contact when it happens, makes a material difference to staying the course. At nume, our clinical team (led by our clinical director) reviews every consultation personally, not through automated scoring, so questions about the evidence behind your treatment get a real answer. If you want to understand more about tirzepatide as a medicine before booking, the tirzepatide overview is a good place to start, and our weight loss treatments page covers the broader landscape. When you are ready, check your eligibility with a free consultation.