How much weight can you lose on Mounjaro?

On average, you can lose up to 22.5% of your body weight on Mounjaro. This was demonstrated in clinical trials over 72 weeks, taken alongside a reduced-calorie diet and more physical activity. The effect depended on the dose. On average, participants lost about 16% of their body weight on the 5mg dose, 21.4% on 10mg, and 22.5% on the highest, 15mg dose. 

Around 9 in 10 people lost at least 5% of their starting weight. How much you lose depends on the dose you reach, how consistently you take it, and the diet and lifestyle changes you make alongside it, so these figures are best treated as a realistic guide rather than a guarantee. 

How Mounjaro works 

Mounjaro is the brand name for tirzepatide, a once-weekly injection. It is a dual agonist, meaning it acts on two gut hormones involved in appetite and blood sugar regulation – GLP-1 and GIP. It reduces appetite and helps you feel full for longer by slowing how quickly the stomach empties, making it easier to eat less. Mounjaro is designed to be used alongside a reduced-calorie diet and regular physical activity for the best results. 

How much weight can you lose? What the trials show 

The headline figures come from SURMOUNT-1, a 72-week trial of around 2,500 adults living with obesity, overweight, with a weight-related health condition, and did not have diabetes. Average weight loss at 72 weeks was:

Almost everyone taking tirzepatide saw a meaningful result: around 89% of people on 5mg, and 96% on 10mg and 15mg, lost at least 5% of their starting weight.

Measured across everyone in the trial, including those who stopped early, the averages are slightly lower, at roughly 15–21%. A higher dose, taken for longer, generally means greater weight loss. Similar results have been seen in SURMOUNT-4 and SURMOUNT-5 with an average weight loss of 20 – 21%. 

Mounjaro weight-loss timeline: what to expect

No two people lose weight at the same pace and it is normal for the figure to fluctuate from week to week.

Here is the average progress seen in studies:

The dosing schedule (and why results build over time) 

You do not start on the highest dose. Everyone begins at the lowest, 2.5mg once a week, which lets your body adjust to the medication rather than driving weight loss on its own. The dose then increases in 2.5mg steps, no sooner than every four weeks, until you reach the dose that works for you — up to a maximum of 15mg. 

Most people settle on 5mg, 10mg or 15mg. This gradual increase is why weight loss tends to build over the first few months, and why side effects are more likely around each step up. If you are losing weight and tolerating a lower dose well, there is no requirement to keep increasing — that is a decision to make with your prescriber. 

What affects how much you lose 

Two people on the same dose can end up with quite different results, and a few factors explain most of the difference. The most important is the dose you reach and can comfortably tolerate. Consistency matters too, as a weekly injection only works if it is taken regularly. Beyond the medication itself, diet and physical activity continue to do a great deal of the work — both in losing weight and in maintaining the results. 

Your starting weight also plays a role, with people who have more to lose often seeing larger changes early on. Other health conditions, medicines, sleep and stress can all influence your results as well. And if the scales stall for a week or two, that is very common and usually temporary — it is worth discussing with your clinician rather than making drastic changes yourself. 

Side effects and safety 

The most common side effects are digestive — nausea, diarrhoea, constipation and, occasionally, vomiting. These are usually mild, tend to appear in the first few weeks and just after a dose increase, and generally settle as your body adjusts. Eating smaller, plain meals and drinking plenty of fluids can help. 

More serious problems are much rarer, but worth being aware of inflammation of the pancreas (pancreatitis) and gallbladder problems can occur, so severe or persistent stomach pain should be checked by a doctor promptly. If you take insulin or a sulfonylurea for diabetes, tirzepatide increases the risk of low blood sugar, so those doses may need adjusting. For more detail, read our full guide to Mounjaro side effects. 

There are two safety points the UK regulator has been particularly clear about: 

Contraception and pregnancy

Mounjaro should not be used during pregnancy, while trying to conceive, or when breastfeeding. It may also reduce how well the contraceptive pill is absorbed, so the MHRA advises anyone using the pill to add a barrier method, or switch to a non-oral method, for four weeks after starting and for four weeks after each dose increase. If you are planning a pregnancy, it should be stopped at least a month beforehand. Your prescriber can advise on the right approach. 

Obtain it only from a registered pharmacy

Mounjaro is a prescription-only medicine and should only be supplied by a UK-registered pharmacy following a proper consultation — not bought as a cosmetic quick fix from unregulated sellers. Any suspected side effects can be reported through the MHRA Yellow Card scheme. 

Who can take Mounjaro in the UK? 

In the UK, Mounjaro is licensed for weight management in adults, used alongside a reduced-calorie diet and increased physical activity. NICE recommends it for obesity where someone has a BMI of 35 or more together with a weight-related health condition — a threshold set 2.5 points lower for people from South Asian, Chinese, other Asian, Middle Eastern, Black African or African-Caribbean backgrounds, who are at higher risk at a lower BMI. 

Access on the NHS is being introduced gradually, with priority currently given to those at highest clinical need — initially a BMI of 40 or more alongside several weight-related conditions — widening over the coming years. Because many people who qualify clinically cannot yet obtain it on the NHS, a private prescription from a regulated online pharmacy, following an online consultation, is a common alternative. In either case, a clinician will first check that it is suitable and safe for you.