Mounjaro Statistics: What the Clinical Numbers Actually Tell You

You've seen the 20% figure, here's where it comes from

Picture someone who weighed 105 kg sitting down with a researcher before starting SURMOUNT-1. Seventy-two weeks later, the average person at the 15mg dose had lost roughly 21–22 kg. That's the real-world translation of the percentage you keep reading about. SURMOUNT-1 enrolled 2,539 participants, all adults with a BMI of 30 or above (or 27-plus with at least one weight-related condition), and none had type 2 diabetes, an important detail, because metabolic disease can affect how the body responds to treatment.

The trial ran three active dose groups: 5mg, 10mg and 15mg, alongside placebo. Average weight loss was around 15% at 5mg, roughly 19% at 10mg and 20–21% at 15mg. Placebo participants lost about 3%, which matters: a lot of people lose a small amount of weight when they're in a clinical trial at all, because lifestyle support is baked in. The medicine's contribution sits above that baseline. Understanding how tirzepatide works at a receptor level helps explain why the results appear stronger than earlier single-pathway medicines.

One other stat worth knowing: around one in three participants at the 15mg dose lost 25% or more of their body weight. That's not the average, it's the upper end of the distribution. Averages smooth out the range, and individual responses genuinely differ. Mounjaro's UK licence covers weight management alongside a reduced-calorie diet and increased physical activity, which reflects how these trials were designed; participants had lifestyle support throughout.

The head-to-head comparison people ask about most

The most common follow-up question after the SURMOUNT-1 figures is: how does Mounjaro compare to Wegovy? SURMOUNT-5, published in the New England Journal of Medicine in 2025, gave the clearest answer yet. It was an open-label trial of 751 adults with obesity and no diabetes, running over 72 weeks. Tirzepatide produced greater average weight loss than semaglutide 2.4mg, the maintenance dose most people associate with Wegovy at the time the trial ran.

The practical implication is that the difference is real and statistically significant, though semaglutide results are still clinically meaningful for many people. NICE's committee discussion in Technology Appraisal 1026 noted that indirect comparisons also favour tirzepatide, and that evidence informed the recommendation. Which medicine suits a particular person, though, remains a clinical question, comorbidities, how someone responds in practice, and tolerance of side effects all count.

It's also worth acknowledging that Wegovy has since had a higher 7.2mg dose approved by the MHRA (January 2026 for the dose itself, with a dedicated single-dose pen following in April 2026), which narrows the efficacy gap somewhat. The landscape is moving quickly, and anyone considering their options should speak to a prescriber with a current picture of the evidence. Our clinical team, including our clinical lead, keeps across exactly this kind of update.

What the statistics don't show, and what to make of that

Clinical trial figures are generated under controlled conditions. Participants are monitored closely, lifestyle support is consistent, and those who drop out are often counted in the final averages using a statistical method called LOCF (last observation carried forward) or similar. Real-world use tends to produce somewhat lower average results, partly because adherence varies and partly because clinical oversight differs. That's not a reason to dismiss the trial numbers (they are the best evidence available) but it's honest context.

The other thing trial averages don't show is the range. Some people lose considerably more than the average, some considerably less. Factors that appear to influence response include starting weight, metabolic health, how consistently someone can follow the dose schedule, and the lifestyle changes made alongside treatment, including whether you're also taking supplements like probiotics alongside Mounjaro, which some people do to support gut comfort during treatment. If you're wondering whether these weight-loss treatment options might be appropriate for your situation, that's exactly the kind of question a prescriber can work through with you properly, much better than reading across from an average to your own circumstances.

One note on the broader programme: SURMOUNT-1 covered participants without diabetes; SURMOUNT-2 included people with type 2 diabetes, where weight loss was somewhat lower (around 15% at 15mg) because diabetes affects how strongly the body responds. The SURPASS programme addressed diabetes management specifically. Together, the clinical programme for tirzepatide involved well over 10,000 participants across SURMOUNT and SURPASS combined, a data set substantial enough to underpin both the UK licence and the NICE recommendation. For the granular figures on any individual trial, the NHS tirzepatide medicines page is a reliable starting point, and the full SURMOUNT-1 paper is freely accessible via the NEJM.

Putting the numbers in the context of getting started

Statistics matter most when you're deciding whether something is worth trying. If you've got a BMI of 30 or above, or 27-plus with a relevant health condition like high blood pressure or obstructive sleep apnoea, you're within the licence criteria for private treatment. Lower thresholds apply for some ethnic backgrounds under UK guidance. But eligibility isn't only about BMI, a prescriber weighs up your full medical picture, any medicines you're already taking (interactions with things like statins are part of that assessment, and you can read more about whether Mounjaro and statins can be taken together if that applies to you), and whether the treatment profile makes sense for you.

Before any prescription is issued, the consultation matters as much as the headline numbers. Similarly, if you're on a course of antibiotics while taking Mounjaro, that's the kind of interaction a prescriber will want to know about before approving treatment. If you order before noon on a weekday, a GPhC-registered prescriber reads your answers that same day, not software, a real clinician. If approved, treatment dispatches the same day and arrives with tracked DPD delivery the next working day. That's the process; the statistics are the reason it's worth going through it. If you're ready to see whether you qualify, you can check your eligibility with a free consultation. If you have questions before then, our FAQs cover the most common ones. And for anything more specific, the team is available seven days a week.