How Much Weight Can You Lose on Mounjaro vs Wegovy: What the Trials Found

Most comparisons between weight management medicines are indirect, drawing on separate trials with different participants and designs. For adults in the UK looking into prescription treatment for obesity or overweight with related health complications, the clearest head-to-head data so far found average weight loss at 72 weeks of 20.2% (22.8 kg) with Mounjaro (tirzepatide) and 13.7% (15.0 kg) with Wegovy (semaglutide), although individual results varied widely.

These two have been compared directly, which is unusual and makes the figures more meaningful than most of what circulates. The numbers are worth reporting properly, including the parts that usually get left out: how many people reached different weight-loss thresholds, how differently men and women responded, when results tended to appear, why progress sometimes slowed, what happened when treatment stopped, and what to know about body composition and side effects.

This page does that. It does not rank the two medicines, because an average across hundreds of people does not determine what any one person will experience, but it does give an evidence-based comparison to help you judge likely outcomes, set realistic expectations, and make better-informed treatment decisions.

Key takeaways: things to know

• In the SURMOUNT-5 trial, average weight reduction at 72 weeks was 20.2% with tirzepatide and 13.7% with semaglutide.
• In absolute terms that was 22.8 kg and 15.0 kg.
• In this trial, women had greater average weight reductions than men on both treatments.
• Both groups contained people who lost a great deal and people who lost very little.
• Weight loss generally builds over time as doses are increased, so early changes may be smaller than the eventual 72-week result.
• Progress slows for almost everyone, which is expected rather than a failure.
• Weight commonly returns after stopping either medicine.

The head-to-head trial

What it tested

SURMOUNT-5 was a phase 3b, open-label, randomised trial in 751 adults with obesity, or with overweight and at least one weight-related complication, who did not have type 2 diabetes.

Participants were assigned to maximum tolerated doses of either mounjaro tirzepatide or semaglutide, given once weekly by injection, alongside a reduced-calorie diet and increased physical activity. This briefly shows how mounjaro works: tirzepatide is a dual receptor agonist that mimics both glp 1 and glucose dependent insulinotropic polypeptide, while semaglutide acts through GLP-1; unlike wegovy, it targets both pathways. Treatment ran for 72 weeks, which is around 17 months.

The primary measure was percentage change in body weight at 72 weeks.

The results

The most commonly reported side effects with both medications were mild to moderate digestive effects, with nausea, constipation, and diarrhea among the other common side effects, and Mounjaro may cause more gastrointestinal effects than Wegovy.

The threshold figures matter more than the averages

The average tells you where the middle of each group sat. The thresholds tell you how many people reached a result that would change their health.

Losing 10% or more of body weight is often associated with clinically meaningful improvements in several obesity-related health measures, although the benefits vary between individuals. Both also contained people who reached 20% and 25%.

That is the more useful way to read these figures than comparing two percentages.

Why averages hide more than they show

An average is a single number standing in for several hundred different outcomes. In both arms of this trial, some participants lost a great deal of weight and some lost very little.

Nothing in the data tells you which group you would fall into. Response varies with factors that are not fully understood, including differences in how individuals respond to these medicines, how much of someone's intake was driven by appetite rather than habit or circumstance, how well they tolerate higher doses, and what else changes alongside treatment.

Results vary between individuals. A trial average cannot predict an individual outcome, and anyone presenting these figures as what you will lose is overstating what the evidence supports.

The sex difference

This is one of the more striking findings and it is rarely reported.

Women lost considerably more than men on both treatments. Average body weight reduction was 23.8% in women and 17.8% in men on tirzepatide, and 18.0% in women and 11.0% in men on semaglutide.

Weight loss was around 6 percentage points lower in men than women in both groups. The trial also included a higher proportion of men than most obesity trials, at 35%, and the trial authors suggested this may explain why overall weight loss appeared slightly lower than in some previous studies.

In this trial, women had greater average weight reductions than men in both treatment groups. This is one reason sex-specific results can provide useful context when interpreting an overall trial average. However, these subgroup findings do not predict how an individual person will respond.

How long before results appear

This is where expectations most often go wrong.

The build-up period

Both medicines are started at lower doses and increased gradually, mainly to improve tolerability. Weight loss generally develops over time rather than appearing all at once.

That means the early weeks are a settling-in period rather than a fair test. Weight change during the first month or two tells you relatively little about where you will end up.

The 24-week marker

A further analysis of the trial looked at who had lost at least 15% of body weight by week 24, describing them as rapid responders. That applied to 44% of participants on tirzepatide and 21% on semaglutide.

Two things follow. A substantial minority saw a large change within six months. And the majority in both groups did not, yet the trial continued for another year, by which point the average figures above were reached.

Being slower to respond at six months is not the same as not responding.

What the trial length tells you

The headline figures are 72-week results. They describe where people were after roughly 17 months of continuous treatment, including the months spent building up the dose.

Judging your own progress at week eight against a 72-week average is not a fair comparison, and it is the most common reason people conclude treatment is not working.

What the trial does not settle

It was open-label. Participants and investigators knew which treatment was being given. That is a recognised limitation, particularly where expectation can influence behaviour and reported outcomes.

It compared maximum tolerated doses. Someone who settles at a lower dose for tolerability is not in the same position as the trial population.

It excluded people with type 2 diabetes, so it does not describe that group. Mounjaro is indicated in the UK for both weight management and type 2 diabetes treatment, but this is one reason these clinical trials do not answer how it performs in the diabetes population.

It ran for 72 weeks. It does not tell you what happens over five years.

It measured weight, not body composition. More on that below.

Effectiveness is only half of a decision. A systematic review and meta-analysis of head-to-head studies found greater weight reduction with tirzepatide and also a higher risk of serious adverse events. In the US, tirzepatide is approved for chronic weight management under the brand name Zepbound, while Mounjaro is the tirzepatide brand used for type 2 diabetes.

What the separate trials showed

For context, each medicine has its own placebo-controlled evidence, from trials with different participants and designs.

Semaglutide was studied in STEP 1, which followed 1,961 participants over 68 weeks and reported average weight loss of 14.9% against 2.4% with placebo. Tirzepatide was studied in SURMOUNT-1, which followed 2,539 participants over 72 weeks, with average weight loss at the highest dose of around 20.9% against around 3.1% with placebo.

These were separate trials rather than a comparison, so the figures should not be placed side by side as if they were. The head-to-head results above are the better basis for understanding how the two differ.

Why progress slows

Almost everyone reaches a point where the scales move more slowly, and it follows from how weight loss works rather than from the medicine failing.

A smaller body requires less energy, both because there is less of it and because energy expenditure falls somewhat further than size alone would predict. At the same time, the body's own appetite signals push back as weight falls.

Eventually intake and expenditure meet at a new level and weight stabilises. That is the system finding a new balance. Maintaining weight loss can be clinically important because sustained weight reduction may help improve several obesity-related health measures.

If progress stalls, the useful questions are whether treatment has been consistent, whether you have reached a dose where most of the effect occurs, and what is happening with protein, activity and sleep. Any ongoing treatment plan should also be reviewed with a healthcare provider, especially if your circumstances change, including if you are pregnant or trying to conceive. Not whether to abandon the treatment.

What happens if you stop

Both medicines supply an appetite signal while they are present. Neither permanently changes how appetite is regulated, so stopping returns appetite to a body that now requires less energy than before. Many people notice appetite returning and food noise becoming louder after stopping because the medicine’s signalling effect is no longer present.

In the STEP 1 extension, participants regained around two thirds of their lost weight within a year of stopping semaglutide, and cardiometabolic improvements reverted towards starting levels for most measures.

SURMOUNT-4 took a different approach with tirzepatide. All 670 participants received treatment for 36 weeks, losing an average of 20.9%, then were randomly assigned to continue or switch to placebo for a further year. Those who switched regained an average of 14.0% of body weight. Those who continued lost a further 5.5%.

Both findings point the same way. These findings show that weight loss achieved during treatment should not automatically be assumed to persist after the medicine is stopped. Long-term weight management may require ongoing treatment, lifestyle support, or both, depending on the individual.

What the figures do not tell you about body composition

Every number on this page is body weight. None of them describes what the weight was made of.

Weight loss can include both fat mass and lean mass. The balance varies between individuals and can be influenced by factors such as diet, protein intake, physical activity and resistance training.

This matters because muscle supports strength, balance and the energy your body uses at rest. Two people reaching the same percentage on the scales can end up in quite different positions depending on what they lost.

For that reason, body weight is only one measure of progress. Waist circumference, strength, physical function and relevant health measures can provide additional information.

Making the numbers useful

1. Compare like with like. Judge your progress against the stage you are at, not against a 72-week average.
2. Use the thresholds, not the mean.A 10% reduction in body weight is often associated with clinically meaningful health improvements, although the benefits vary between individuals.
3. Adjust for the sex difference if you are comparing yourself to a headline figure.
4. Track something besides weight. Strength, waist measurement and how you feel through the day.
5. Judge over months. Weight fluctuates with fluid, salt and digestive contents, so a single reading says little.
6. Expect a plateau and decide in advance that it is not a reason to stop.

Red flags

Seek urgent medical attention for severe and persistent stomach pain that may spread through to your back, with or without nausea and vomiting, as this can be a sign of pancreatitis; swelling of the face, lips, tongue or throat; difficulty breathing; allergic reactions; or signs of significant dehydration.

Contact your prescriber if weight loss is much faster than expected, if you are eating very little and feel persistently exhausted, if you experience severe symptoms after starting treatment or after dose increases, or if you are losing strength noticeably.

Reading your own progress

The figures on this page are useful for understanding what these medicines can do across a population. They are a poor yardstick for a single person at week six.

If you want a fair read on your own progress, give it months rather than weeks, compare against the stage of treatment you are actually at, and track something alongside the scales that tells you what you are losing. That last point matters more than any percentage, and it is the one most people only think about afterwards.

Medical Disclaimer

This article is for general information only. It is not medical advice and it does not replace the patient information leaflet supplied with your medicine or an individual assessment by an appropriately qualified healthcare professional.

Wegovy and Mounjaro are prescription-only medications. They should only be used under the supervision of an appropriately qualified healthcare provider, with ongoing support during treatment, following a clinical assessment that considers your medical history, current medicines and other conditions.Treatment suitability depends on an individual clinical assessment, including medical history, current medicines and other health conditions.

All trial results described here are averages from specific study populations at defined doses and durations. They cannot predict an individual outcome, and results vary between individuals.

These medicines are not recommended during pregnancy. If you are pregnant, planning a pregnancy or become pregnant while taking treatment, speak with your prescriber for advice.

Do not start, stop or change a prescribed medicine, or alter your dose, without advice. Seek urgent medical attention for severe and persistent stomach pain that may spread to your back, swelling of the face, lips, tongue or throat, difficulty breathing, or signs of significant dehydration.