Mounjaro in the UK: The Complete Guide to Tirzepatide for Weight Loss

Mounjaro is the brand name for tirzepatide, a once-weekly injection licensed in the UK for weight management in adults with obesity, or with overweight plus at least one weight-related health condition. It works on two gut-hormone pathways (GIP and GLP-1) to reduce appetite and help people eat less, and in clinical trials it produced larger average weight loss than any previously licensed weight-loss medicine. It is prescription-only, available through the NHS in a phased rollout and through regulated private providers, and it is meant to be used alongside changes to diet and activity, not instead of them.

This guide brings together what UK adults most often want to know: what Mounjaro is, who it is licensed for, what the evidence shows, how dosing works, what side effects to expect, and how NHS and private access differ. It links out to our more detailed guides on each topic, and back to the Mounjaro hub for a quick overview.

What is Mounjaro?

Mounjaro is made by Eli Lilly and contains the active ingredient tirzepatide. It was first licensed to treat type 2 diabetes, and in November 2023 the Medicines and Healthcare products Regulatory Agency (MHRA) extended the licence to cover weight management. In the UK it comes as the Mounjaro KwikPen, a multi-dose pre-filled pen that holds four weekly doses.

Tirzepatide belongs to a newer group of medicines sometimes called "dual agonists" or "twincretins". Most of the weight-loss injections that came before it, such as liraglutide (Saxenda) and semaglutide (Wegovy), act on one hormone receptor: the GLP-1 receptor. Tirzepatide acts on two: the GLP-1 receptor and the GIP receptor. That dual action is thought to be one reason it produced larger average weight loss in trials, although researchers are still working out exactly how much each pathway contributes.

Mounjaro and tirzepatide: are they the same thing?

Yes. Tirzepatide is the medicine; Mounjaro is the brand name used in the UK and most other countries. In the United States, tirzepatide is also sold for weight loss under the brand name Zepbound, but that brand is not used in the UK. If you see "tirzepatide" on an NHS letter or prescription, it refers to the same active ingredient as Mounjaro. For more on the molecule itself, see our guide to tirzepatide in the UK.

How does Mounjaro work?

GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) are hormones your gut releases after you eat. Among other things, they signal to the brain that you have eaten, help the pancreas release insulin when blood sugar rises, and slow the rate at which food leaves the stomach.

Tirzepatide mimics both hormones, but it lasts far longer than the natural versions, which is why a single weekly injection is enough. In practice, people taking it commonly describe:

• feeling full sooner and for longer after meals
• thinking about food less often, sometimes described as quieter "food noise"
• finding it easier to eat smaller portions without feeling deprived

These effects help people eat less, which leads to weight loss. Tirzepatide also improves blood sugar control, which is why it was first developed for type 2 diabetes. Our detailed explainer, How Mounjaro works, covers the biology in more depth, including what is and is not yet understood about GIP.

Who is Mounjaro licensed for in the UK?

The UK licence (set out in the Summary of Product Characteristics, or SmPC) covers weight management, including weight loss and weight maintenance, in adults alongside a reduced-calorie diet and increased physical activity, when they have:

• a BMI of 30 kg/m² or more (obesity), or
• a BMI of 27 to under 30 kg/m² (overweight) plus at least one weight-related health condition, such as prediabetes or type 2 diabetes, high blood pressure, abnormal blood fats (dyslipidaemia), obstructive sleep apnoea or cardiovascular disease.

Being within the licence does not mean someone will be prescribed it. A prescriber must also check that there are no reasons it would be unsafe, and that it is an appropriate choice given your other medicines, health conditions and goals. You can use our BMI calculator or eligibility checker to understand where you sit, but they are informational only and do not replace a clinical assessment.

Who should not take Mounjaro?

The SmPC lists hypersensitivity to tirzepatide or any of the ingredients as a reason not to use it. Beyond that, prescribers take particular care, and may advise against treatment, in situations including:

• pregnancy, planning a pregnancy, or breastfeeding
• a history of pancreatitis
• severe gastrointestinal disease, including severe gastroparesis (delayed stomach emptying)
• diabetic eye disease (retinopathy) in people with diabetes, as rapid improvements in blood sugar have been linked with temporary worsening
• a personal or family history of medullary thyroid cancer or multiple endocrine neoplasia type 2, which US labelling highlights because of findings in rodent studies
• a current or past eating disorder

Our guide to who shouldn't take GLP-1 medications explains these in more detail.

What the evidence shows

Tirzepatide's weight-loss licence rests mainly on the SURMOUNT trial programme. The headline findings are summarised below; for a fuller week-by-week picture, see Mounjaro results: what the trials show over time.

A few points help put these numbers in context:

• They are averages. In SURMOUNT-1, most participants on tirzepatide lost at least 5% of their body weight, but individual results ranged widely.
• People with type 2 diabetes tend to lose less. This pattern is seen with all GLP-1-based medicines and is reflected in the SURMOUNT-2 results.
• Trials include structured support. Participants received regular lifestyle counselling, which may not always be matched in everyday care.
• Weight loss is gradual. Most of the loss happened over the first year or so, with weight tending to level off towards the end of the 72 weeks.

Longer-term follow-up of SURMOUNT-1 participants who had prediabetes, published in 2025, found that weight loss was largely sustained over about three years of continued treatment and that tirzepatide substantially reduced the risk of developing type 2 diabetes compared with placebo.

How Mounjaro is taken

Mounjaro is injected under the skin (subcutaneously) once a week, on the same day each week, at any time of day, with or without food. Recommended injection sites are the stomach area (at least 5cm from the belly button), the front of the thigh, or the back of the upper arm if someone else is giving the injection. Rotating the site each week helps reduce skin reactions.

The dose schedule

Treatment starts low and increases gradually. This is called titration, and its main purpose is to give your digestive system time to adjust, which reduces side effects.

Not everyone needs or tolerates the maximum dose. Many people stay at a lower dose if they are losing weight steadily and side effects are manageable. Your prescriber should review progress before each increase. Our Mounjaro dosing guide explains how these decisions are made, and our KwikPen guide walks through the injection steps. If you miss an injection, the rule in the product information depends on how many days have passed; see missed a Mounjaro dose?.

Side effects and safety

Like all medicines, Mounjaro can cause side effects. Most are digestive and are related to the way it slows stomach emptying and acts on appetite pathways.

Common side effects

In the SURMOUNT-1 trial, the most frequently reported side effects were:

• nausea
• diarrhoea
• constipation
• vomiting
• indigestion and acid reflux
• reduced appetite
• abdominal pain or bloating
• tiredness
• injection-site reactions such as redness or itching

These were mostly mild to moderate and tended to occur during the dose-escalation period. A small proportion of participants stopped treatment because of side effects. Practical steps that many people find helpful include eating smaller meals, stopping when full, avoiding very fatty or greasy foods, and drinking enough fluids. Our guide to Mounjaro side effects covers management in detail, and you can also see the side effects topic page.

Serious but less common risks

• Acute pancreatitis. Inflammation of the pancreas has been reported with GLP-1-based medicines. The typical warning sign is severe, persistent pain in the upper abdomen that may spread to the back, with or without vomiting.
• Gallbladder problems. Gallstones and gallbladder inflammation are more likely during rapid weight loss.
• Dehydration and kidney problems. Severe vomiting or diarrhoea can lead to dehydration, which in turn can affect kidney function.
• Low blood sugar. This is uncommon in people without diabetes but is a risk for people also taking insulin or sulfonylureas.
• Aspiration during anaesthesia. Because Mounjaro slows stomach emptying, you should tell the medical team if you are due to have surgery or a procedure under sedation or general anaesthetic.

Pregnancy and contraception

Mounjaro should not be used during pregnancy. The SmPC advises stopping it at least one month before a planned pregnancy. It may also make oral contraceptive pills less reliable, particularly at the start and after each dose increase, so the product information recommends considering a non-oral method or adding a barrier method for four weeks after starting and after each increase. The MHRA has reinforced these messages in its safety communications. See our guide to GLP-1s and contraception for more detail.

How to access Mounjaro in the UK

There are two main routes to treatment: the NHS and private prescribing services, including regulated online pharmacies.

On the NHS

NICE recommended tirzepatide for managing overweight and obesity in technology appraisal TA1026, published in December 2024. NICE recommends it for adults with a BMI of at least 35 kg/m² and at least one weight-related condition, with lower thresholds for people from certain ethnic backgrounds who face higher health risks at lower BMIs.

Because of the very large number of people who meet these criteria, NHS England agreed a phased rollout. Prescribing in primary care began in June 2025 for people with a BMI of 40 or more and at least four of five qualifying conditions (type 2 diabetes, high blood pressure, dyslipidaemia, obstructive sleep apnoea and cardiovascular disease). A second group, with a BMI of 35 to 39.9 and four or more of those conditions, became eligible from June 2026, and further groups are expected to follow in later years. Arrangements vary between areas and between the four UK nations. Our guide to Mounjaro on the NHS explains the criteria and how to ask about access.

Privately

Many people who meet the licence criteria but not the current NHS criteria use private prescribing services. A legitimate provider should:

• be registered with the General Pharmaceutical Council (GPhC) and, where a prescribing service is involved, with the Care Quality Commission (CQC) in England or its equivalent elsewhere in the UK
• carry out a proper medical consultation and check your weight, typically using photo or video verification
• ask about your medical history and other medicines, and may contact your GP
• provide ongoing monitoring, not just a one-off supply

Medicines bought outside the regulated system, such as from social media sellers or beauty salons, may be fake, contaminated or wrongly dosed. Our guide to fake and unlicensed weight-loss jabs explains the warning signs. You can see how regulated providers compare on service, support and safety checks on our providers page.

What affects the cost of private treatment?

We do not quote prices in our guides because they change frequently. The main factors that affect what you pay privately are:

• the dose, because higher strengths generally cost more, especially since Eli Lilly raised UK list prices for private supply in September 2025
• whether consultation, monitoring and delivery are bundled into the price or charged separately
• needles and sharps bins, which are not included in the Mounjaro pack and may or may not be included by the provider
• subscription terms, minimum commitments and how price changes are passed on

On the NHS, tirzepatide is supplied under the standard NHS prescription arrangements for each UK nation. For current private price ranges, see our Mounjaro prices page, and for the background, our Mounjaro price guide.

Lifestyle support still matters

Mounjaro is licensed as an addition to a reduced-calorie diet and increased physical activity, and NICE expects it to be used alongside wraparound support. There are good reasons for this beyond the licence wording:

• Protein and strength work help protect muscle. A meaningful share of the weight lost on GLP-1-based medicines can come from lean tissue, so adequate protein and resistance exercise are commonly advised.
• Smaller appetites need better nutrition. Eating less makes it more important that what you do eat provides enough protein, fibre, vitamins and minerals.
• Habits support the long term. Weight regain after stopping is common, and established habits may help limit it.

See our guides on what to eat on GLP-1 medication and exercise on GLP-1 medication for practical advice.

Long-term treatment and stopping

Obesity is increasingly recognised as a long-term, relapsing condition, and the evidence suggests that the effects of tirzepatide on appetite fade when it is stopped. In SURMOUNT-4, participants who switched to placebo after 36 weeks of tirzepatide regained a substantial share of their lost weight over the next year, while those who continued kept losing weight.

That does not mean everyone must take it indefinitely, but it does mean decisions about stopping, stepping down or continuing should be planned with a prescriber. Newer research, including the SURMOUNT-MAINTAIN study presented in 2026, has looked at whether a lower maintenance dose can help limit regain. Our Mounjaro maintenance guide covers the options.

How Mounjaro compares with other options

Mounjaro is one of several medicines licensed for weight management in the UK. The main alternatives are:

• Wegovy (semaglutide injection), a once-weekly GLP-1 injection with evidence of cardiovascular benefit from the SELECT trial. See Mounjaro vs Wegovy.
• Saxenda (liraglutide), an older once-daily GLP-1 injection, generally associated with smaller average weight loss.
• Oral GLP-1 tablets. At the time of writing, the MHRA has authorised the Wegovy tablet (oral semaglutide) and Foundayo (orforglipron) for weight management, both in 2026. NHS availability depends on NICE appraisals, so check the latest SmPC and NICE guidance. See our oral GLP-1 hub.
• Orlistat, a tablet that reduces fat absorption, with more modest average weight loss.

Which is most suitable depends on your health, preferences and what your prescriber recommends. You can explore side-by-side comparisons of providers and services on our compare pages.

When to speak to a professional

Talk to your GP, pharmacist or prescriber before starting Mounjaro, before changing your dose, and before stopping. You should also contact them if:

• side effects such as nausea, vomiting or diarrhoea are stopping you from eating or drinking normally
• you are not losing weight as expected, or you are losing weight very quickly
• you become pregnant or are planning a pregnancy
• you are starting any new medicine, or are due to have surgery or a procedure under anaesthetic
• you notice changes in your mood, or thoughts that worry you

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

• severe, persistent abdominal pain, especially pain that spreads to your back, with or without vomiting (possible pancreatitis)
• pain in the upper right abdomen with fever or yellowing of the skin or eyes (possible gallbladder problems)
• signs of severe dehydration, such as very little urine, dizziness or confusion
• signs of a serious allergic reaction, such as swelling of the face, lips or throat, or difficulty breathing

You can report suspected side effects to the MHRA through the Yellow Card scheme.