Mounjaro vs Wegovy: An Evidence-Based Comparison

Mounjaro (tirzepatide) and Wegovy (semaglutide) are the two most widely used weekly injections for weight management in the UK. Both reduce appetite and are taken alongside a reduced-calorie diet and more physical activity. The key differences are that Mounjaro acts on two hormone receptors (GIP and GLP-1) while Wegovy acts on one (GLP-1), and that in the SURMOUNT-5 head-to-head trial, people taking Mounjaro lost more weight on average. Wegovy, however, has proven cardiovascular benefits from the SELECT trial and a longer track record. This guide sets out the evidence on both so you can discuss them with a prescriber.

At a glance

For a full introduction to each medicine, see our complete guide to Mounjaro and complete guide to Wegovy, and the Mounjaro hub.

How they work

Wegovy: a GLP-1 receptor agonist

Semaglutide copies glucagon-like peptide-1 (GLP-1), a hormone released by the gut after eating. It acts on receptors in the brain to reduce hunger and increase fullness, slows stomach emptying, and helps the pancreas release insulin when blood glucose is high. Semaglutide has been modified to last about a week in the body, allowing weekly dosing. It is the same molecule as Ozempic, which is licensed for type 2 diabetes; see Ozempic vs Wegovy.

Mounjaro: a dual GIP and GLP-1 receptor agonist

Tirzepatide is a single molecule that activates both GLP-1 receptors and GIP (glucose-dependent insulinotropic polypeptide) receptors. GIP is another gut hormone involved in insulin release and energy balance. The precise contribution of GIP to weight loss is still being researched, but combining the two actions appears to produce a greater effect on appetite and weight than GLP-1 activation alone. Our guide to how Mounjaro works explains this in more detail.

What the trials show

The main placebo-controlled trials

These trials were run separately, in different groups of people, so they cannot be compared directly. They did suggest that tirzepatide at higher doses might lead to greater weight loss, which SURMOUNT-5 was designed to test.

SURMOUNT-5: the head-to-head trial

SURMOUNT-5, published in the New England Journal of Medicine in 2025, is the most important evidence for comparing the two medicines. It randomly assigned 751 adults with obesity (and without type 2 diabetes) to tirzepatide or semaglutide, each at the maximum tolerated dose (tirzepatide 10mg or 15mg; semaglutide 1.7mg or 2.4mg), for 72 weeks.

A larger proportion of people on tirzepatide reached higher thresholds of weight loss, such as 15%, 20% and 25%. The trial was funded by Eli Lilly, which makes Mounjaro, and was open-label, meaning participants knew which medicine they were taking. It was conducted in the United States and Puerto Rico. These points do not invalidate the findings, but they are worth knowing. Our in-depth analysis of SURMOUNT-5 covers its strengths and limitations.

Higher-dose Wegovy

In January 2026, the MHRA authorised a maximum Wegovy dose of up to 7.2mg weekly for adults with obesity (a BMI of 30 or more). In the STEP UP trial, average weight loss at 72 weeks was nearly 21% with 7.2mg, compared with about 17.5% with 2.4mg, in a trial population with a higher starting weight than some other trials. This higher dose has not been compared head to head with tirzepatide. It does not apply to people with a BMI below 30 or to the cardiovascular indication. Whether it is suitable is a prescriber's decision.

Heart health and other outcomes

SELECT and Wegovy

The SELECT trial (NEJM, 2023) followed more than 17,600 adults with overweight or obesity and established cardiovascular disease, but without diabetes, for an average of over three years. Semaglutide 2.4mg reduced the risk of major adverse cardiovascular events (cardiovascular death, non-fatal heart attack or non-fatal stroke) by 20% compared with placebo. Wegovy's UK licence was updated to reflect this. See Wegovy and heart health.

Tirzepatide outcome trials

Tirzepatide has extensive trial data in type 2 diabetes (the SURPASS programme) and in obesity (SURMOUNT). A cardiovascular outcomes trial in people with type 2 diabetes compared it with another GLP-1 medicine, and a dedicated cardiovascular outcomes trial in people with obesity without diabetes was ongoing at the time of writing. Tirzepatide has also been studied in obstructive sleep apnoea and heart failure with preserved ejection fraction. Check the current SmPC for licensed indications.

What this means

For someone with established heart disease, the cardiovascular outcome evidence for semaglutide may be an important consideration. For someone whose main goal is weight reduction, the larger average weight loss with tirzepatide may weigh more heavily. Both factors are part of the conversation with a prescriber.

Side effects compared

The two medicines share a very similar side-effect profile, because both act on GLP-1 receptors.

"Very common" in an SmPC means affecting more than 1 in 10 people; "common" up to 1 in 10; "uncommon" up to 1 in 100. Check the current SmPC for precise categories.

In SURMOUNT-5, gastrointestinal side effects were the most frequent in both groups, mostly mild to moderate and concentrated during dose escalation. Slightly fewer people stopped tirzepatide because of them. It is difficult to know how much this reflects the medicines themselves and how much the dose-escalation schedules used in the trial.

Both medicines carry the same important warnings: pancreatitis, gallbladder disease, dehydration leading to kidney problems, low blood sugar when combined with insulin or sulfonylureas, and possible worsening of diabetic retinopathy. The MHRA has advised effective contraception during treatment, and noted that tirzepatide may reduce the effectiveness of oral contraceptives in some people, particularly around the start of treatment and dose increases, so additional or non-oral contraception may be advised. For full detail, see Mounjaro side effects and Wegovy side effects.

Dosing compared

Both medicines start with a low dose and increase every four weeks or more, to give the gut time to adjust.

With Mounjaro, the SmPC describes maintenance doses of 5mg, 10mg or 15mg, and people do not always need to reach the highest dose. With Wegovy, 2.4mg is the standard maintenance dose, with 1.7mg an option if 2.4mg is not tolerated. Your prescriber and the current SmPC are the authority for your schedule. See Mounjaro doses explained and Wegovy doses explained.

The pens

Both are supplied in multi-dose pre-filled pens in the UK: the Mounjaro KwikPen and the Wegovy FlexTouch pen. Each pen contains several weekly doses, and the technique is a little different for each. See our guides to using the Mounjaro KwikPen and using the Wegovy FlexTouch pen.

Who can be prescribed each?

Licensed criteria

Both medicines are licensed for adults with a BMI of 30 or more, or 27 or more with at least one weight-related condition (such as type 2 diabetes, high blood pressure, abnormal blood fats, obstructive sleep apnoea or cardiovascular disease), alongside a reduced-calorie diet and increased physical activity. Wegovy is also licensed for some adolescents aged 12 and over, subject to criteria in the SmPC. Check the SmPCs for full details.

NHS access

In practice, NHS access is limited and varies by area. Our guides to Mounjaro on the NHS and Wegovy on the NHS explain how to find out what is available locally.

Who should not take either

Both are generally unsuitable during pregnancy or breastfeeding, and caution or avoidance applies with a history of pancreatitis, severe gastrointestinal disease, a personal or family history of medullary thyroid cancer, or some eating disorders. See who should not take GLP-1 medications.

Which might a prescriber consider?

There is no single "right" answer. These are examples of the factors a prescriber may weigh, not recommendations.

Factors that may point towards Mounjaro

• Wanting the larger average weight loss seen in SURMOUNT-5
• Not reaching treatment goals on semaglutide
• Difficulty tolerating semaglutide (although tolerability varies between individuals)
• Type 2 diabetes, where tirzepatide also has strong evidence on blood glucose control

Factors that may point towards Wegovy

• Established cardiovascular disease, given the SELECT evidence and licence
• Preference for a medicine with a longer track record in weight management
• Being under 18, where Wegovy has an adolescent licence
• Preference for a tablet option within the same medicine, as Wegovy tablets are now authorised
• Eligibility for an NHS specialist service offering semaglutide

Factors that affect both

• Personal medical history and other medicines
• Cost and access, privately or on the NHS
• Previous experience with either medicine
• Personal preference after discussing the evidence

What both medicines need to work well

Whichever medicine is prescribed, the trials that led to their licences combined the medicine with support to change diet and activity. The UK licences for both specify use alongside a reduced-calorie diet and increased physical activity. In practice, several things help:

• Enough protein. Eating much less can mean losing muscle as well as fat. Including protein at each meal helps protect muscle; see protein on weight loss injections.
• Strength training. Resistance exercise two or more times a week supports muscle and bone; see preserving muscle on GLP-1 treatment.
• Fluids. Reduced thirst and gastrointestinal side effects can lead to dehydration.
• Smaller, slower meals. These help reduce nausea and reflux with both medicines.
• Regular reviews. A prescriber should check progress, side effects and dose at intervals, and consider changes if treatment is not working as hoped.

It is also worth having realistic expectations. Weight loss with both medicines usually happens gradually over many months and tends to level off. Some people respond much less than average; our guide to what to do if GLP-1 treatment doesn't work for you covers the options.

Long-term treatment and stopping

Both medicines work for as long as they are taken. Withdrawal trials show what happens on stopping:

• STEP 4 (JAMA, 2021): after 20 weeks on semaglutide, people switched to placebo regained a substantial part of their lost weight over the following year, while those who continued kept losing weight.
• SURMOUNT-4 (JAMA, 2024): after 36 weeks on tirzepatide, people switched to placebo regained a significant proportion of their weight, while those who continued maintained or increased their loss.

This is why obesity is increasingly treated as a long-term condition. Decisions about how long to continue, whether to reduce the dose, and how to stop should be made with a prescriber. See Mounjaro maintenance, Wegovy maintenance and stopping and weight regain after stopping GLP-1 medication.

Switching between them

People switch for many reasons: side effects, not reaching goals, cost, supply or access changes. There is no official dose conversion between semaglutide and tirzepatide. Prescribers typically consider the current dose, how well it is tolerated and how much time has passed since the last dose, and often start the new medicine at a lower dose and increase it again. You should never take both medicines together. See switching from Wegovy to Mounjaro and switching from Mounjaro to Wegovy.

Cost: what affects it

We do not quote prices in our guides because they change frequently. Factors that affect private costs include:

• Manufacturer list prices. The UK list price of Mounjaro rose in September 2025, which led to price changes across private providers.
• Dose. Many providers charge more for higher doses, particularly for Mounjaro.
• Provider pricing models. Some include consultations, clinical support and delivery; others charge separately.
• Supply. Pen availability and pack sizes can affect pricing.
• Treatment length. Because both medicines are often taken long term, the overall cost over a year or more matters more than a single month.

For current comparisons, see our prices page and the guide to the long-term cost of GLP-1 treatment.

Safety when getting treatment privately

Both Mounjaro and Wegovy are prescription-only medicines. In the UK they should only be supplied after a consultation with a registered prescriber, from a pharmacy registered with the General Pharmaceutical Council (GPhC). Be wary of anyone offering either medicine without a proper assessment, or of "pens" sold on social media or through beauty salons. The MHRA has seized large quantities of fake and unlicensed weight-loss injections. See getting weight loss injections online safely and fake and unlicensed weight loss jabs.

When to speak to a professional

Speak to your GP, pharmacist or prescriber before starting, switching or stopping either medicine, and if you are not sure which might suit you. Tell them about any history of pancreatitis, gallbladder disease, thyroid cancer, kidney problems, diabetic eye disease or eating disorders, all the medicines you take (including contraception), and whether you are pregnant, planning pregnancy or breastfeeding.

Seek urgent medical help through NHS 111, or call 999 in an emergency, if you experience:

• Severe, persistent abdominal pain, especially if it spreads to your back, with or without vomiting (possible pancreatitis)
• Pain in the upper right abdomen, fever, or yellowing of the skin or eyes (possible gallbladder problems)
• Vomiting or diarrhoea that stops you keeping fluids down, or signs of dehydration such as very little urine, dizziness or confusion
• Signs of a severe allergic reaction, such as swelling of the face, lips or throat, or difficulty breathing
• Symptoms of low blood sugar if you also take insulin or a sulfonylurea

You can report suspected side effects to the MHRA through the Yellow Card scheme. To compare regulated services, see our provider comparison or compare providers side by side.