Short answer: Mounjaro (tirzepatide) is licensed by the MHRA for weight management in adults with a BMI of 30 or above, or 27 or above with a weight-related condition, so its safety has been assessed for those people. Its most common side effects are nausea, diarrhoea, constipation and vomiting, mostly mild to moderate and most likely while the dose is going up; serious problems such as pancreatitis are uncommon (up to 1 in 100 people). It is not suitable for everyone, including anyone who is pregnant, which is why a prescriber checks your health before it is supplied. The MHRA warns that pens bought without a prescription may be fake and unsafe.
This guide sets out what the UK product information and the MHRA say, as of October 2026: who Mounjaro is licensed for, who should not take it, how common each side effect is, the serious risks to know about, the long-term evidence, and how to avoid fake pens.
Is Mounjaro licensed and approved in the UK?
Yes. The MHRA authorised Mounjaro for weight management in adults on 8 November 2023, when it was already used for type 2 diabetes, and approved the four-dose KwikPen used in the UK on 25 January 2024.
A licence means the MHRA has assessed the evidence on a medicine's quality, safety and effectiveness and approved it for specific uses, judging that its benefits justify its risks for the people it is licensed for. It does not mean a medicine is safe for everyone, or for any use. The MHRA says it has not assessed the safety of GLP-1 medicines used outside their licence, for example for weight loss in people who are not obese or overweight, and that they should not be used to lose weight for cosmetic reasons.
Mounjaro also carries the black triangle (▼). It is under additional monitoring, so new safety information can be identified quickly. Our guide to how Mounjaro works explains what it does in the body.
Who is Mounjaro licensed for?
For weight management, the licence covers adults with a BMI of 30 or above, or 27 to under 30 with at least one weight-related condition, alongside a reduced-calorie diet and more physical activity. Its safety for weight management has not been established in anyone under 18. These are the conditions our pharmacist looks for.
Who treatment may suit
Treatment may be suitable if you're aged 18–85 and have a BMI of 30 or above, or a BMI of 27–29.9 alongside one of the following: high blood pressure, raised cholesterol or blood fats, obstructive sleep apnoea, cardiovascular disease, prediabetes, or type 2 diabetes.
Who should not take Mounjaro?
The UK product information lists one contraindication: an allergy to tirzepatide or any of the other ingredients. It also says Mounjaro should not be used during pregnancy. We do not supply Mounjaro if, for example, you are pregnant, planning a pregnancy or breastfeeding, have had pancreatitis, have type 1 diabetes, or if you or a blood relative have had medullary thyroid cancer (MTC) or multiple endocrine neoplasia type 2 (MEN2).
The table shows what the product information says about each situation, and what we do.
| If you | The UK product information | Our service |
|---|---|---|
| Are allergic to tirzepatide or any ingredient | Must not be used: its one contraindication | We do not supply |
| Are pregnant or planning a pregnancy | Should not be used in pregnancy. Stop at least 1 month before a planned pregnancy | We do not supply |
| Are breastfeeding | Its current text says it "could be considered". The MHRA says GLP-1 medicines should not be taken while breastfeeding | We follow the MHRA and do not supply |
| Have had pancreatitis | Not studied after pancreatitis, so to be used with caution | We do not supply |
| Have type 1 diabetes | Its diabetes licence is for type 2 diabetes | We do not supply |
| Have had medullary thyroid cancer or MEN2, or a blood relative has | Thyroid C-cell tumours were seen in rats. The relevance to people is unknown | We do not supply |
| Have gastroparesis or another severe stomach or bowel condition | Not studied in severe gastrointestinal disease, so to be used with caution | We do not supply if you have gastroparesis or have had a bowel obstruction |
| Take insulin or a sulphonylurea, such as gliclazide | Higher risk of low blood sugar. The other medicine's dose may need lowering | We do not start Mounjaro through our service. Your GP or diabetes team needs to manage it |
| Have proliferative diabetic retinopathy | Diabetic retinopathy needs close monitoring | We do not start treatment through our service. It needs your diabetes team or GP first |
| Are due an operation under general anaesthetic or deep sedation | Risk of stomach contents entering the lungs | We do not start treatment in the 7 days before it |
| Have had weight loss surgery in the last 24 months | Not mentioned | We do not supply until 24 months after it |
| Are under 18, or over 85 | Not established under 18 for weight management. Very limited data at 85 or over | We supply adults aged 18 to 85 |
Our consultation also asks about severe liver, kidney or heart disease, current cancer treatment, eating disorders and current gallbladder problems, and some of those answers mean we cannot supply Mounjaro either. If you have type 2 diabetes, our guide explains how Mounjaro fits with other diabetes medicines.
Wondering whether Mounjaro suits you? Our consultation asks about your health and the medicines you take, and a GPhC-registered pharmacist reviews every answer before anything is supplied.
Check your eligibilityWho needs extra care on Mounjaro?
Some people can take Mounjaro but need it to be watched more closely. Tell your pharmacist if any of these apply to you.
Kidney or liver problems. No dose change is needed, but experience in severe kidney or liver disease is limited, so the product information advises caution. The KwikPen also contains benzyl alcohol (5.4mg in each dose), which can cause allergic reactions and, in people with liver or kidney problems, can build up over time and make the blood too acidic (metabolic acidosis).
Older age. The product information says older people may be more likely to have complications from dehydration, and there is very little data in people aged 85 or over.
Other medicines taken by mouth. Mounjaro slows how quickly your stomach empties, which can change how tablets are absorbed, most of all when you start and after each dose increase. The product information advises monitoring medicines that need careful dosing, such as warfarin and digoxin, at those times.
Gallstones in the past. In the trials, gallbladder problems were linked to greater weight loss. Tell us about past gallstones so your pharmacist can review them.
Heart rate. In the weight management trials, resting heart rate rose by an average of 3 beats a minute. Tell us about any heart condition.
Alcohol. The NHS says it is best to avoid alcohol while using tirzepatide, because it can make feeling or being sick worse. See Mounjaro and alcohol.
What are the side effects of Mounjaro?
The side effects reported most often are stomach and bowel effects. The UK product information groups every side effect by how often it happened in the clinical trials, and these are the frequencies from the weight management trials.
| How common | Side effects |
|---|---|
| Very common (more than 1 in 10 people) | Nausea, diarrhoea, vomiting, constipation, stomach pain and a smaller appetite. In people with type 2 diabetes who also take a sulphonylurea or insulin, low blood sugar |
| Common (up to 1 in 10 people) | Tiredness, dizziness, low blood pressure, indigestion, bloating, burping, wind, reflux, hair loss, allergic reactions such as a rash or itching, redness or itching where you inject, gallstones, and raised pancreatic enzyme (lipase) or calcitonin levels in blood tests |
| Uncommon (up to 1 in 100 people) | Acute pancreatitis, an inflamed gallbladder (cholecystitis), slower stomach emptying, a faster pulse, pain where you inject, a changed sense of taste and changes in skin sensation |
| Rare (up to 1 in 1,000 people) | Severe allergic reactions (anaphylaxis and angioedema), from reports after the medicine was launched |
In the two main weight management trials (SURMOUNT-1 and SURMOUNT-2), stomach and bowel side effects were reported by 55.6%, 55.8% and 55.6% of people on 5mg, 10mg and 15mg, compared with 29.7% on placebo. Most were mild (61.0%) or moderate (34.4%), they were most common while the dose was being increased, and 1.9%, 3.3% and 4.3% of people stopped treatment because of them, compared with 0.5% on placebo. Individual results vary.
Our guide to Mounjaro side effects covers what to expect at each dose and what helps.
What are the serious side effects of Mounjaro?
Serious side effects are much less common, but they are the ones to know before you start.
| Risk | How common | What the evidence says |
|---|---|---|
| Acute pancreatitis (an inflamed pancreas) | Uncommon, up to 1 in 100 people | There have been rare reports of severe and fatal cases, and the MHRA strengthened its warnings in January 2026. If pancreatitis is confirmed, Mounjaro must never be restarted |
| Gallbladder problems | Gallstones common; an inflamed gallbladder uncommon | Acute gallbladder problems affected 2.0% of people on tirzepatide and 1.6% on placebo, and were linked to greater weight loss |
| Dehydration and kidney problems | No frequency given | Sickness, diarrhoea and nausea can cause dehydration, which can affect how well the kidneys work, including sudden kidney failure |
| Low blood sugar | Very common with a sulphonylurea or insulin, in type 2 diabetes | The risk is mainly when Mounjaro is taken with those medicines, whose dose may need lowering |
| Diabetic eye disease | No frequency given | In people with diabetic retinopathy, a fast improvement in blood sugar has been linked to it getting worse for a time |
| Stomach contents entering the lungs under anaesthesia | No frequency given | Cases have been reported with GLP-1 medicines, because the stomach can still hold food despite fasting |
| Severe allergic reaction | Rare, up to 1 in 1,000 people | Anaphylaxis and angioedema have been reported since launch |
To put pancreatitis in context, the MHRA received 1,296 UK Yellow Card reports of pancreatitis with GLP-1 medicines as a group, Mounjaro included, between 2007 and October 2025, 19 of them fatal. It estimates that about 25.4 million packs of these medicines were dispensed in the past 5 years.
On eyesight, the MHRA has linked semaglutide (the medicine in Wegovy and Ozempic) to an eye condition called NAION, in very rare reports, and says it is reviewing the evidence for other GLP-1 medicines. As of October 2026 it is not listed in the Mounjaro product information. Any sudden loss of vision needs same-day help, as below.
When to get help: our pharmacist's advice
Stop your treatment and seek urgent medical help if you experience: severe, persistent stomach pain, especially spreading to your back, with or without vomiting. This can be a sign of pancreatitis. Sudden pain in the upper right of your tummy, fever, or yellowing of the skin or eyes: possible gallbladder problems. Sudden loss of vision, or loss of part of your field of vision: seek same-day eye assessment. Swelling of the face or lips, difficulty breathing, or a widespread rash: call 999.
The signs that need prompt advice, such as dehydration, are in the safety box at the end of this guide.
Is Mounjaro safe in pregnancy, and does it affect the pill?
No, Mounjaro must not be used in pregnancy. There is not enough information on its effects on an unborn baby, and animal studies showed harm. It can also make the contraceptive pill less reliable for a few weeks at a time.
Pregnancy: these medicines must not be used in pregnancy. Stop and contact us or your GP immediately if you become pregnant. If planning pregnancy: stop Mounjaro at least 1 month before, Wegovy at least 2 months before.
Contraception (Mounjaro only): tirzepatide can reduce absorption of the contraceptive pill. Use a non-oral method or add condoms for 4 weeks after starting and for 4 weeks after each dose increase. Wegovy needs no extra precautions unless severe vomiting or diarrhoea occurs, then follow missed-pill guidance.
The MHRA says GLP-1 medicines should not be taken while breastfeeding. Our guides cover contraception and pregnancy on GLP-1 treatment and Mounjaro and breastfeeding in full.
Is it safe to have an operation while taking Mounjaro?
It can be, as long as your surgical and anaesthetic team knows. Because Mounjaro slows how quickly your stomach empties, food and drink can stay in your stomach despite fasting, and during general anaesthesia or deep sedation they could enter your airways and lungs. The MHRA asks anaesthetists to assess this risk for each patient, and advises keeping taking your medicine as usual unless your doctor tells you otherwise.
Before any operation: tell your surgical or anaesthetic team you take a GLP-1 medicine. It slows stomach emptying, which matters for anaesthesia.
If you are due an operation within 7 days, we will not start Mounjaro until after it.
Can Mounjaro cause depression?
Depression is not listed as a side effect in the UK product information for Mounjaro. The MHRA's guidance on GLP-1 medicines, which include Mounjaro, says a comprehensive safety review found that the available data does not support a causal link between GLP-1 medicines and depression, suicidal thoughts or suicide, and that it will keep monitoring this. Our consultation asks about your mental health, and if your mood changes during treatment, speak to your pharmacist or GP. Our guide on whether Mounjaro can cause depression goes into the evidence.
Is Mounjaro safe long term?
The UK licence sets no maximum length of treatment, and the evidence now covers several years. Here is what the longest trials found.
- SURMOUNT-1, 176 weeks. In the longest weight management results (New England Journal of Medicine, 2025), 1,032 adults with obesity and prediabetes took tirzepatide or placebo for 176 weeks. The most common side effects were stomach and bowel effects, mostly mild to moderate and mainly during the first 20 weeks while the dose was being increased, and no new safety concerns were found.
- SURPASS-CVOT, a median of 4 years. This trial (New England Journal of Medicine, 2025) was in 13,299 adults with type 2 diabetes and heart or circulation disease, so it tells us most about that group. It compared tirzepatide with dulaglutide, another weekly diabetes injection. A heart attack, stroke or death from heart disease happened to 801 people (12.2%) on tirzepatide and 862 (13.1%) on dulaglutide, which met the trial's test that tirzepatide was no worse. Side effects were similar overall, with more stomach and bowel effects on tirzepatide. Individual results vary.
- Thyroid. In 2-year studies in rats, tirzepatide caused thyroid C-cell tumours at every dose tested. The product information says the relevance of this to people is unknown, and a 6-month study in mice found no increase. We do not supply Mounjaro if you or a blood relative have had medullary thyroid cancer or MEN2.
Your treatment is reviewed regularly, weighing how well it is working for you against any side effects. Our guide on staying on Mounjaro long term explains what the licence and NICE say about how long to take it.
How do you come off Mounjaro safely?
Talk to your prescriber first, and do not stop suddenly without advice: the NHS says stopping can affect your blood sugar if you have type 2 diabetes, and that your dose may be reduced gradually. Mounjaro leaves the body over several weeks (its half-life is about 5 days), appetite returns as it clears, and most people regain some weight after stopping, as the SURMOUNT-4 trial (JAMA, 2024) showed. Our guide to what happens when you stop taking Mounjaro covers coming off it step by step.
What has the MHRA said about Mounjaro safety?
These are the MHRA's main safety communications that cover Mounjaro, as of 17 October 2026.
| Date | What the MHRA said |
|---|---|
| 8 November 2023 | Mounjaro authorised for weight management in adults, alongside a reduced-calorie diet and more physical activity |
| September 2024 | A review found the evidence does not support a link between GLP-1 receptor agonists and suicidal thoughts, self-harm or depression |
| 24 October 2024 | A reminder that stomach side effects can lead to severe dehydration and hospital stays, a warning about misuse for cosmetic weight loss, and that some fake GLP-1 medicines have been found to contain insulin |
| 28 January 2025 | A warning about stomach contents entering the lungs during general anaesthesia or deep sedation |
| 5 June 2025 | Guidance for patients, including effective contraception on GLP-1 medicines and backing up the pill on Mounjaro |
| 29 January 2026 | Strengthened warnings on acute pancreatitis, including rare necrotising and fatal cases |
| 5 February 2026 | Semaglutide linked to NAION in very rare reports; other GLP-1 medicines under review. The patient guidance was updated |
| 24 February 2026 | Fake Mounjaro KwikPen 15mg pens, batch D873576, found supplied through one UK online pharmacy |
| 24 July 2026 | Do not increase your dose to speed up weight loss, avoid fake medicines, and retatrutide is not authorised in the UK |
| 15 October 2026 | Over 12,000 fake retatrutide and tirzepatide pens seized in Birmingham |
Are fake Mounjaro pens dangerous?
Yes. The MHRA says it has had reports of people having severe side effects from fake GLP-1 medicines. A fake medicine may contain the wrong ingredients, no active ingredient or harmful substances, and some fake GLP-1 medicines have been found to contain insulin. Fake pre-filled pens can closely copy the real ones.
- 14 October 2026. Over 12,000 fake retatrutide and tirzepatide pens, and packaging for about 30,000 more, were seized from an industrial unit in Birmingham, worth about £2 million.
- 28 May 2026. About 12,000 doses of unlicensed weight loss medicines, including retatrutide and tirzepatide, were recovered from a country estate near Northampton.
- February 2026. Fake Mounjaro KwikPen 15mg pens labelled with batch D873576, a genuine batch number for the 7.5mg pen, were found supplied through one UK online pharmacy. They contained tirzepatide, but could not be confirmed sterile. They came to light because of faults with the pens: in all but one case, the dose knob came off during use.
- October 2025. The first illegal weight loss medicine production site found in the UK was shut down, and 5,000 unauthorised retatrutide and tirzepatide pens were seized.
How to protect yourself:
- Get Mounjaro only on a prescription from a registered pharmacy, after a consultation about your health.
- Genuine weight-loss medicines come as pre-filled pens or tablets. Powder in a vial that you mix yourself is never an authorised product.
- Never buy from social media, a salon, or anyone who doesn't ask about your health first. If you're offered one without a prescription, walk away.
- Retatrutide is not authorised in the UK, so anyone selling it is doing so illegally. See our retatrutide guide.
- If a pen looks damaged or doesn't work, don't use it and don't try to get the medicine out. Keep it, message us and report it on the Yellow Card site.
Every medicine we supply is bought from its manufacturer or a UK-licensed wholesaler. Our safety page explains how to check your medicine is genuine and how to check any online pharmacy.
How does a pharmacist check Mounjaro is safe for you?
You answer health questions online. Our consultation asks about your height and weight, your medical history, the medicines you take, your mental health, any planned operations, pregnancy and breastfeeding.
A pharmacist reviews every answer. A GPhC-registered pharmacist reviews every consultation before anything is supplied, and some answers mean we cannot supply Mounjaro. If your pharmacist cannot approve your order, we refund you in full.
You start low and step up slowly. If you are new to Mounjaro, you start on 2.5mg once a week, the licensed starting dose, and each increase comes after at least 4 weeks on your current dose. Your pharmacist reviews you before each increase.
A health check before every reorder. Each reorder starts with a short health check, and any answer that needs it goes to your pharmacist before anything is sent.
Genuine medicine from a registered pharmacy. QuickCare Pharmacy, the pharmacy behind Solira, is on the GPhC register as 9013213, and buys every medicine from its manufacturer or a UK-licensed wholesaler.
Your GP, if you agree. We ask whether you would like us to tell your GP about your treatment, and only do so with your consent.
How can you use Mounjaro as safely as possible?
Take the dose you are prescribed, no more. The MHRA warns against increasing your dose to speed up weight loss. Our guide shows how to inject Mounjaro step by step.
Never use the medicine left in a pen. Each KwikPen holds four doses, and the MHRA says not to try to get out any medicine left after them. See the "golden dose".
Drink plenty of fluids. The MHRA advises staying well hydrated throughout treatment, because sickness and diarrhoea can lead to dehydration.
Tell every doctor, dentist and anaesthetist. The MHRA notes that a private prescription may not appear in your medical records, so mention Mounjaro whenever you are treated.
Switch medicines only with advice. The MHRA says to speak to a healthcare professional before switching between GLP-1 medicines, because they differ in strength and how they are used. See switching between Mounjaro and Wegovy.
Tell us how you are getting on. The NHS advises speaking to a pharmacist or doctor about side effects that bother you or do not go away, so message your pharmacist if they do.
How do you report a side effect from Mounjaro?
Report a suspected side effect, or a pen you think may not be genuine, on the MHRA Yellow Card website or app. Mounjaro carries the black triangle (▼), so it is under additional monitoring, and the MHRA says reports of side effects, even ones already known, add to what is known about how often they happen and how severe they are. Please tell us too, so your pharmacist can review your treatment. Our safety page has the links.