Mounjaro Results: What the Trials Show Over Time

In clinical trials, Mounjaro (tirzepatide) produced average weight loss of about 15% to 21% of body weight over 72 weeks, depending on dose, compared with about 3% on placebo. Weight usually falls gradually over the first few months as the dose is increased, continues steadily through most of the first year, and tends to level off somewhere between 12 and 18 months. People with type 2 diabetes tend to lose less, results vary widely between individuals, and weight is commonly regained if treatment stops. Alongside weight, trials show improvements in blood pressure, blood sugar, blood fats and some weight-related conditions.

This guide walks through the SURMOUNT trial programme, explains what the results look like over time, and sets out why your own experience may differ from the averages. For a broader introduction, see our complete guide to Mounjaro in the UK or the Mounjaro hub.

Understanding trial results before you read them

A few points make the numbers easier to interpret:

• Percentages are of starting body weight. Losing 20% from 110kg is 22kg; from 90kg it is 18kg.
• Results are averages. Within any group, some people lost far more and some lost little.
• There are different ways of analysing trials. The "treatment-regimen" estimand counts everyone randomised, including those who stopped treatment. The "efficacy" estimand estimates the effect in people who kept taking the medicine as intended, and produces larger numbers. Where we quote figures below, we use the more conservative treatment-regimen estimates unless stated.
• Participants had lifestyle support. Trials included regular counselling on diet and activity, which may differ from routine care.

SURMOUNT-1: the pivotal trial

SURMOUNT-1, published in the New England Journal of Medicine in 2022, enrolled 2,539 adults with a BMI of 30 or more, or 27 or more with at least one weight-related condition, who did not have diabetes. Participants were randomly assigned to weekly tirzepatide 5mg, 10mg or 15mg, or placebo, for 72 weeks, alongside a reduced-calorie diet and increased physical activity.

Approximate treatment-regimen figures from the SURMOUNT-1 publication.

Participants on tirzepatide also had larger reductions in waist circumference, blood pressure, fasting insulin and blood fats than those on placebo, and many with prediabetes at the start returned to normal blood sugar levels.

The shape of the weight-loss curve

In SURMOUNT-1, average weight in the tirzepatide groups fell steadily from the early weeks, with the curves beginning to flatten in the later part of the 72-week trial. Weight in the placebo group changed little. This general shape, a steady decline that gradually levels off, is typical of effective weight-loss medicines.

What results look like over time

The table below describes the typical pattern seen in trials. It is a general guide, not a prediction for any individual.

Early response

In SURMOUNT-4, all participants first took tirzepatide at their maximum tolerated dose (10mg or 15mg) for 36 weeks before being randomised. During that lead-in period, average weight loss was about 21%. That gives a sense of how much of the total effect can occur within the first nine months or so for people who reach higher doses.

The plateau

As weight falls, the body needs fewer calories and makes adaptive changes that increase appetite. At some point, the reduced food intake on tirzepatide matches the body's new, lower energy needs, and weight stabilises. In trials, this typically happened somewhere between 12 and 18 months. See our guide to weight loss plateaus on GLP-1 medication for what this means and what prescribers may consider.

Longer-term results: three years

A three-year analysis of SURMOUNT-1 participants who had prediabetes at the start was published in the New England Journal of Medicine in 2025. Over about 176 weeks of treatment:

• weight loss was largely sustained, at around 12% (5mg), 19% (10mg) and 20% (15mg), compared with about 1% on placebo
• the risk of progressing to type 2 diabetes was reduced by roughly 94% compared with placebo
• after treatment stopped at the end of the study, some regain occurred and diabetes risk rose again

These findings support the idea that tirzepatide's benefits persist while treatment continues. See our guide to long-term GLP-1 use.

Results in people with type 2 diabetes: SURMOUNT-2

SURMOUNT-2, published in The Lancet in 2023, studied adults with obesity or overweight and type 2 diabetes. After 72 weeks, average weight loss was about 13% on 10mg and 15% on 15mg, compared with about 3% on placebo. Blood sugar control also improved substantially.

People with type 2 diabetes consistently lose less weight on GLP-1-based medicines than people without diabetes. The reasons are not fully understood but may include differences in metabolism, the effects of other diabetes medicines and reduced glucose loss in the urine as blood sugar improves. See GLP-1 medication and type 2 diabetes.

After lifestyle change: SURMOUNT-3

SURMOUNT-3, published in Nature Medicine in 2023, asked whether tirzepatide adds to weight loss already achieved through an intensive lifestyle programme. Participants who lost at least 5% of their weight over a 12-week lead-in were then randomised to tirzepatide or placebo. Over the following 72 weeks, those on tirzepatide lost around an additional 18% of their weight, while those on placebo regained a small amount. This suggests tirzepatide can build on, rather than replace, lifestyle changes.

What happens when treatment stops: SURMOUNT-4

SURMOUNT-4, published in JAMA in 2024, is one of the most important trials for understanding long-term results.

People who switched to placebo regained a substantial share of what they had lost, although on average they remained below their starting weight at 88 weeks. Improvements in blood pressure, cholesterol and blood sugar also partly reversed. These results are similar to those seen with semaglutide in the STEP 4 trial.

More recent research has explored ways to limit regain. SURMOUNT-MAINTAIN, presented at the European Congress on Obesity in May 2026, found that stepping down to tirzepatide 5mg after reaching the maximum tolerated dose limited regain compared with placebo, although continuing the maximum tolerated dose was most effective. See our Mounjaro maintenance guide and our guide to weight regain after stopping GLP-1 medication.

Tirzepatide vs semaglutide: SURMOUNT-5

SURMOUNT-5, published in the New England Journal of Medicine in 2025, was a head-to-head trial of 751 adults with obesity, without diabetes, comparing the maximum tolerated dose of tirzepatide (10mg or 15mg) with the maximum tolerated dose of semaglutide (1.7mg or 2.4mg) over 72 weeks.

Digestive side effects were the most common adverse events in both groups. See SURMOUNT-5: the head-to-head trial and our Mounjaro vs Wegovy comparison.

Health results beyond weight

Obstructive sleep apnoea

The SURMOUNT-OSA trials, published in the New England Journal of Medicine in 2024, found that tirzepatide substantially reduced the number of breathing interruptions per hour of sleep in adults with obesity and moderate-to-severe obstructive sleep apnoea, compared with placebo. See tirzepatide and obstructive sleep apnoea.

Heart failure with preserved ejection fraction

The SUMMIT trial, also published in 2024, studied adults with obesity and a type of heart failure called heart failure with preserved ejection fraction. Tirzepatide reduced the combined risk of cardiovascular death or worsening heart failure events and improved symptoms and physical limitations compared with placebo.

Blood pressure, blood fats and blood sugar

Across the SURMOUNT trials, tirzepatide was associated with improvements in blood pressure, triglycerides and other blood fats, and markers of blood sugar control. These improvements generally track with weight loss and partly reverse if weight is regained.

Putting percentages into kilograms

Percentages can feel abstract. The table below converts some trial averages into kilograms for illustrative starting weights. These are arithmetic examples, not predictions for any individual.

Even a 5% to 10% loss is associated with meaningful improvements in blood pressure, blood sugar and other health markers for many people. Health benefits do not depend on matching the trial averages.

How Mounjaro results compare with other treatments

Trials of different medicines enrolled different people, used different durations and were run at different times, so cross-trial comparisons should be made cautiously. With that caveat, the main placebo-controlled trials give a broad sense of scale.

The only large head-to-head trial, SURMOUNT-5, found greater average weight loss with tirzepatide than with semaglutide. Newer oral options, including the Wegovy tablet and Foundayo (orforglipron), were authorised by the MHRA in 2026; their trial results come from different populations and durations, so check the current SmPC for details. See Every UK weight loss injection compared.

Why individual results vary

Several factors are linked with how much weight someone loses:

• Type 2 diabetes: typically associated with smaller losses.
• Dose reached: higher doses produced more weight loss on average.
• Time on treatment: results build over many months.
• Adherence: missed doses and breaks reduce the effect.
• Other medicines: some medicines, such as certain antidepressants, antipsychotics and steroids, can promote weight gain.
• Diet, activity, sleep and stress: these still influence results.
• Biology: genetics and hormonal factors play a part that is not yet fully understood.

A small proportion of people lose little weight despite reaching an adequate dose. NICE TA1026 advises NHS prescribers to review whether to continue if less than 5% of initial weight has been lost after six months on the highest tolerated dose. See What if GLP-1 treatment doesn't work for you? and realistic weight loss expectations on GLP-1 treatment.

What the trials do not tell us

Clinical trials are the most reliable way to measure whether a medicine works, but they have limits that are worth bearing in mind:

• Who took part. Trial participants met specific criteria and were often healthier in other respects than the wider population of people with obesity. Some groups, including older adults with multiple conditions and some ethnic groups, may be under-represented.
• Support levels. Regular study visits and lifestyle counselling may have helped participants stay on treatment and make changes.
• Duration. Most trials lasted 72 weeks; three-year data exist for some participants, but evidence over decades is not yet available.
• Adherence. In real life, missed doses, supply interruptions and cost-related breaks are more common than in trials.
• Outcomes. Trials of weight loss measure weight and risk factors. Trials designed to show reductions in heart attacks, strokes or deaths in people without diabetes are still under way for tirzepatide at the time of writing.

Real-world studies are beginning to report on how tirzepatide performs in routine care, and NICE has said it will review the NHS access criteria as the rollout progresses. See long-term GLP-1 use.

How trials measure body composition

Some smaller studies within the SURMOUNT programme used scans to measure how much of the weight lost came from fat and how much from lean tissue. Broadly, most of the weight lost was fat, but a meaningful proportion was lean mass, which includes muscle. This is a pattern seen with weight loss by most methods, and it is why protein intake and strength training are commonly emphasised. See preserving muscle mass on GLP-1 treatment.

Making sense of your own progress

Rather than comparing yourself with trial averages or social media posts, it can help to:

• track trends over several weeks rather than day-to-day changes
• look beyond the scales: waist measurement, blood pressure, energy, mobility and blood results all matter
• note how your appetite and eating habits have changed
• share your progress honestly with your prescriber at reviews

See measuring progress beyond the scales. Regulated providers vary in how often they review progress and how they support people through plateaus; our providers page compares these service features, and our prices page explains how ongoing costs are structured.

When to speak to a professional

Speak to your prescriber, GP or pharmacist if:

• you have lost less than you expected after several months on a stable dose
• you are losing weight very quickly, or struggling to eat and drink enough
• you are thinking about stopping or reducing treatment
• you have type 2 diabetes and your blood sugar readings are changing, especially if you take insulin or a sulfonylurea
• you notice changes in mood or eating behaviour that concern you

Seek urgent medical help (NHS 111, or 999 in an emergency) if you have:

• severe, persistent abdominal pain, which may spread to your back, with or without vomiting
• pain in the upper right abdomen with fever or yellowing of the skin or eyes
• signs of severe dehydration, such as very little urine, dizziness or confusion