Biggest Weight Loss on Mounjaro: What the Trial Data Shows (October 2026)

01 · The core answer

What is the biggest weight loss on Mounjaro?

On the 15mg dose, people lost on average 20.9% of their body weight, while people on lifestyle changes alone lost 3.1%.² That is the benchmark to use when you read any claim about maximum results.

You may see higher figures quoted online, including the 'top responder' numbers that some summaries repeat. Those describe the best individual outcomes, not what to expect.

The trial data also shows how many people reached large losses. At 72 weeks, 85% of participants on 5mg, 89% on 10mg and 91% on 15mg had lost at least 5% of their body weight. Half of participants on 10mg and 57% on 15mg lost at least 20% of their body weight.² So large losses are common on higher doses in a trial setting, but they are not universal.

Read this alongside our guides to Mounjaro expected weight loss and realistic weight loss on Mounjaro, which set out what a typical journey looks like rather than the best case.

02 · What moves the number

What separates a bigger result from an average one?

Several factors move your outcome up or down, and most are within your influence.

The takeaway is that the biggest results come from the whole package: an effective dose, patience, and habits that support a lower calorie intake. The medicine reduces appetite; you still decide what to do with that.

03 · Your next step

Should you aim for the biggest result?

Aim for the best sustainable result for your health, not the largest number on a chart. A prescriber will usually think about your starting point, your conditions, your side effects and your goals before increasing a dose. Chasing a record can mean tolerating more side effects than you need to.

If you are thinking about starting, our weight loss clinic explains how treatment works. You can see current strengths and prices on the Mounjaro pen page; the 2.5mg starter pen costs £169.99 per month at the standard price, and new customers save £40 on their first order with code FIRST40. All six doses are in stock.

04 · SURMOUNT-1 results

What SURMOUNT-1 actually found

SURMOUNT-1 is the main trial behind most weight-loss figures you see for Mounjaro. In the SURMOUNT-1 trial of 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone.²

These are trial averages. Individual results vary, and treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.² That wording matters. An average is the middle of a spread, so about as many people sit above it as below it.

A worked example makes the percentage easier to picture. For someone starting at 100 kg, 20.9% is about 21 kg. Someone starting heavier would lose more kilograms from the same percentage, and someone starting lighter would lose fewer. That is why a 'biggest loss in kilograms' headline often says more about the person's starting weight than about the medicine.

Mounjaro is the brand name for tirzepatide, a once-weekly injectable prescription medicine made by Eli Lilly. In the UK it is licensed for weight management in adults and for type 2 diabetes. It comes as a pre-filled multi-dose pen (KwikPen) in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹

05 · Why results differ

Why some people lose far more than others

People respond differently because bodies, appetites, medical histories and daily routines differ. The trial gives a clear picture of that spread. At 72 weeks, 85% of participants on 5mg, 89% on 10mg and 91% on 15mg had lost at least 5% of their body weight. Half of participants on 10mg and 57% on 15mg lost at least 20% of their body weight.²

Read that the other way round and it is just as informative. Not everyone reached the larger thresholds, even on the highest dose, and some people lost less than the average. If you are one of them, that is not a sign that you are doing something wrong; it is within the normal range of responses.

Online accounts of dramatic results are a poor guide. People who lose the most are the most likely to post about it, so the loudest stories are not representative. Trial averages, with their stated durations, are the fairer measure. Our page on Mounjaro predicted weight loss goes further into how to use those averages without over-reading them.

06 · Dose and titration

Does a higher dose mean a bigger result?

On average, yes: in SURMOUNT-1 the average loss rose from 5mg to 10mg to 15mg.² But the dose you end up on is decided with your prescriber, not chosen from a chart.

The aim of the early steps is tolerability. Starting low gives your body time to adjust, and your prescriber can hold you at a strength that works and that you can live with. Some people find a middle strength gives them a good result with fewer side effects than the maximum would. That is a perfectly good outcome, and it is not a failure to reach the top dose.

If you want to understand a middle strength, see our guide to Mounjaro 7.5mg for weight loss. For the full range of what the medicine can do, our Mounjaro weight loss overview is a good starting place.

Dose decisions belong with your prescriber, who reviews you as treatment goes on.

07 · How it works

How Mounjaro produces weight loss

Tirzepatide is a dual-action medicine that works on two natural gut-hormone receptors, GIP and GLP-1. Together these help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin. In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹

This is the reason the result depends so much on behaviour. The medicine lowers the pull of food, but it does not burn fat by itself. People who use the quieter appetite to eat more regularly, choose filling foods and stay active tend to be the ones closest to the trial averages.

08 · Slow progress

What if you are not losing as much as you hoped?

Slower-than-hoped progress is common and does not mean the medicine has failed. Trial results are measured over 72 weeks, so judging your own progress after a short time can mislead you. Weight loss is rarely a straight line; there are quicker stretches and flatter ones.

Check the basics first: are you taking the injection on schedule, are you eating enough to feel well but not more than you need, and are you staying active? If those are in place and you are still concerned, speak to your prescriber at your monthly review. They can look at your dose, side effects and routine together.

Ask your prescriber for advice that fits you. Treat claims that a supplement can boost your results with suspicion; low-cost supplements come with no clinical oversight and do not replace a licensed medicine.

If you notice any new symptom, tell your prescriber, and you can report a suspected side effect through the Yellow Card scheme.¹⁹ The patient information leaflet lists the known side effects.¹³

09 · Serious side effects

Serious side effects: when to get help straight away

Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. If you take insulin or a sulfonylurea alongside Mounjaro, watch for low blood sugar (shakiness, sweating, confusion) — your prescriber may need to adjust those medicines.¹

10 · NHS or private

Getting Mounjaro through the NHS or privately

Mounjaro is available on the NHS, but access is being phased in over several years. NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first (initially BMI 40+ with four or more qualifying conditions).⁴ Full rollout is expected to take years, which is why many people who meet the licensed criteria choose regulated private treatment rather than waiting.

Private treatment is supplied only after an online consultation reviewed by a GPhC-registered prescriber. Our service is registered with the GPhC (9012878), and our Mounjaro comes through official LillyDirect supply, sourced directly from Eli Lilly. We provide a free consultation, free next-day tracked delivery and ongoing monthly reviews. See Mounjaro prescribed for weight loss and our UK pharmacy prescription service for how it works.

Mounjaro (tirzepatide) is a prescription-only medicine. It is used alongside a reduced-calorie diet and increased physical activity. Individual results vary. This page is information, not a substitute for medical advice.