Wegovy vs Mounjaro: which is better for weight loss?

If you’re thinking of taking weight-loss medicine, you’ve probably heard of the brand names Mounjaro and Wegovy.

Mounjaro (tirzepatide) and Wegovy (semaglutide) injections are prescribed to aid weight loss in combination with diet and exercise.

They’re both GLP-1 agonists, which work by tricking the brain into thinking you’re full, so you eat less. They do this by mimicking a hormone called GLP-1 (glucagon-like peptide-1) that’s released after eating.

However, Mounjaro also mimics another hormone that regulates appetite called GIP (glucose-dependent insulinotropic polypeptide) – so it works in 2 ways.

Is Wegovy or Mounjaro better for weight loss?

Research suggests that Mounjaro is more effective for weight loss than the Wegovy injection.

A head-to-head trial published in the New England Journal of Medicine (NEJM) in May 2025 gave 751 people with obesity who did not have type 2 diabetes a weekly injection of either Mounjaro or Wegovy for around a year and a half.

The US researchers found:

• those on Mounjaro lost 20.2 per cent of their body weight
• those on Wegovy lost 13.7 per cent of their body weight.

People given Mounjaro also saw their waist sizes shrink over 5cm (around 2 inches) more on average than those on Wegovy.

Looking specifically at heart health, only Wegovy (semaglutide) is currently approved in the UK to reduce the risk of serious heart problems in people with obesity.

A 2023 study in the NEJM of 17,604 people who already had a cardiovascular disease found that Wegovy cut the risk of dying from coronary heart disease or having a heart attack or stroke by 20 per cent after almost 3 years compared to a dummy injection.

And a review of 19 different weight-loss medicines with 99,791 people in the British Medical Journal (BMJ) in July 2026 found the Wegovy injection had the strongest evidence for reducing major heart problems.

Compared to lifestyle changes alone, the Wegovy injection reduced the risk of a heart attack by 28 per cent after 57 weeks.

But the research did show that both Wegovy and Mounjaro lowered the risk of developing heart failure by 57 per cent and 51 per cent respectively after 1 year.

• Read more about the most effective weight-loss medicines.

What about the Wegovy pill?

There has not yet been a trial comparing the weekly Mounjaro injection with the daily Wegovy pill.

The tablet, which was recently approved in the UK, but is not yet available on the NHS, contains the same active ingredient as the Wegovy injection (semaglutide). There is not a pill version of Mounjaro.

The July 2026 review in the BMJ showed that, while the Wegovy pill was slightly more effective than the Wegovy injection for weight loss, Mounjaro was still more effective.

Compared to lifestyle changes alone after 1 year, people lost:

• 14.9 per cent of their body weight on the Mounjaro injection
• 10.9 per cent on the Wegovy pill
• 9.8 per cent on the Wegovy injection.

Which is safer, Wegovy or Mounjaro?

Studies suggest that a similar amount of people experience side effects on each drug.

In the NEJM’s 2025 head-to-head trial, researchers found that around the same number of people experienced side effects or adverse events on the Wegovy or Mounjaro injection.

Between 77 per cent and 79 per cent reported at least 1 side effect – most commonly digestive problems such as feeling sick, constipation or diarrhoea.

Overall, around 6 per cent of people taking Mounjaro and 8 per cent of those taking Wegovy stopped taking the injections before the end of the study due to side effects.

And the 2026 review in the BMJ found a similar number of participants stopped taking the Wegovy pill or Mounjaro injection due to side effects – around 28 per 1,000.

This was slightly lower in those taking the Wegovy injection – around 20 per 1,000 people using the medicine.

Common side effects of GLP-1 agonists include:

• digestive problems
• headaches
• dizziness
• gallstones
• hair loss
• an increased risk of an inflamed pancreas (acute pancreatitis).

However, semaglutide, the active ingredient in the Wegovy pill and injection, has also been linked to very rare cases of NAION (non-arteritic anterior ischaemic optic neuropathy), which causes sudden loss of vision in 1 eye at a time.

Can you switch from Mounjaro to Wegovy, or vice versa?

If you’re taking Mounjaro or the Wegovy injection or pill and thinking of switching to a different medicine, speak to your doctor or pharmacist first.

They can advise you on the right dose to start on, and how long you should wait after your last dose before starting the new one.

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