You cannot take Mounjaro (tirzepatide) if you are pregnant, planning pregnancy or breastfeeding, have type 1 diabetes, a personal or family history of medullary thyroid cancer or MEN2, a history of pancreatitis, severe gastrointestinal disease, an active eating disorder, severe liver or kidney impairment, or a known allergy to tirzepatide. It is also not licensed for anyone under 18.
Below, a UK pharmacist's perspective on each contraindication — what it is, and why it rules Mounjaro out. These checks exist to keep treatment safe, which is why every prescription follows a clinical consultation rather than an instant online purchase.
What is Mounjaro and how does it work?
Mounjaro is a weekly self-injection containing tirzepatide. It activates two gut-hormone receptors at once — GLP-1 and GIP — which reduce appetite, slow how quickly the stomach empties and help you feel fuller for longer.
Because it acts on digestion, metabolism and (in diabetes) blood sugar, certain existing conditions change how safely it can be used. That is the reason the contraindications below matter.
Who cannot take Mounjaro — the full list
Mounjaro is a Prescription-Only Medicine. It is not suitable for you if any of the following apply.
1. Pregnancy, planning pregnancy, or breastfeeding
Mounjaro is not recommended in pregnancy or while breastfeeding, because its safety for a developing baby or infant has not been established. If you could become pregnant, you should use reliable contraception during treatment.
If you are planning a pregnancy, it is generally advised to stop Mounjaro well in advance and discuss timing with your prescriber.
2. Personal or family history of medullary thyroid carcinoma (MTC) or MEN2
Multiple Endocrine Neoplasia syndrome type 2 (MEN2) is an inherited condition that raises the risk of a specific thyroid cancer (medullary thyroid carcinoma). GLP-1-based medicines carry a thyroid-tumour warning, so a personal or family history of either is a firm contraindication.
This is one of the clearest "do not take" categories — be sure to disclose any family thyroid-cancer history during your consultation.
3. A history of pancreatitis
Acute pancreatitis (inflammation of the pancreas) is a rare but serious potential side effect of this class of medicine. If you have had pancreatitis before, Mounjaro is not suitable because of the risk of recurrence.
Warning signs to act on at any point during treatment include severe, persistent stomach pain that may spread to your back, often with vomiting. Seek urgent medical help if this happens.
4. Type 1 diabetes
Mounjaro is not for people with type 1 diabetes. It is used for weight management and, separately, type 2 diabetes — it is not a substitute for insulin and should not be used in place of insulin therapy.
5. Severe gastrointestinal disease
Because Mounjaro slows stomach emptying and commonly causes nausea, diarrhoea, constipation and vomiting, severe pre-existing GI disease (such as significant gastroparesis or severe inflammatory bowel conditions) makes it unsuitable.
6. Active eating disorder
An appetite-suppressing medicine is not appropriate alongside an active eating disorder, as it may worsen disordered eating and nutrition. Supportive care is the priority here, not weight-loss medication.
7. Severe liver or kidney impairment
Severe liver or kidney impairment affects how your body handles medicines and how it copes with side effects such as dehydration from vomiting or diarrhoea. In these cases Mounjaro is not recommended.
8. Known allergy to tirzepatide
If you have had a serious allergic reaction to tirzepatide or any ingredient in Mounjaro, you must not use it. Severe allergic reactions are rare but are a medical emergency.
9. Under 18
Mounjaro is licensed for adults aged 18 and over only.
Conditions that need caution, not an automatic "no"
Some situations do not rule out Mounjaro outright but call for careful prescriber judgement and sometimes closer monitoring:
- Diabetic retinopathy — rapid improvements in blood sugar can be associated with worsening retinopathy, so eye health may need monitoring.
- Use with insulin or sulfonylureas — combining these can increase the risk of low blood sugar (hypoglycaemia); doses may need adjusting.
- History of gallstones — rapid weight loss can raise gallstone risk.
- Other regular medicines — because Mounjaro slows gastric emptying, it can affect how some medicines are absorbed. Tell your prescriber about everything you take.
These are exactly the details a registered prescriber weighs up at your free online consultation before deciding whether treatment is appropriate.
Who may be eligible for Mounjaro?
Mounjaro may be considered if you are 18 or over and have:
- a BMI of 30 or above (obesity); or
- a BMI of 27–30 with a weight-related condition such as type 2 diabetes, high blood pressure or sleep apnoea.
Meeting the BMI threshold does not guarantee a prescription. A treatment is prescribed only if it is clinically appropriate and safe for you after review. You can read more on the Mounjaro page or compare it with other options on our treatments overview.
What the evidence shows
In the SURMOUNT-1 trial, participants on the 15mg dose lost on average 22.5% of body weight over 72 weeks, alongside lifestyle support. Individual results vary; not everyone reaches this.
Mounjaro does not cure obesity or any condition — it is a tool used alongside changes to diet and activity, under ongoing prescriber support.
If Mounjaro isn't right for you
If a contraindication applies, there may still be safe options to discuss. Our prescribers can talk you through alternatives such as the Wegovy injection or the once-daily Wegovy Tablet — though these share much of the same GLP-1 safety profile and many of the same contraindications, so eligibility is always assessed individually. You can also view all weight-loss injections in one place.
Common side effects to be aware of
Even when Mounjaro is suitable, side effects are common. More than 1 in 10 people experience nausea, diarrhoea, constipation, vomiting, decreased appetite or fatigue — these often ease as your body adjusts during gradual dose increases.
Rare but serious effects include severe allergic reaction, acute pancreatitis, severe hypoglycaemia, severe GI disease and worsening diabetic retinopathy. If you experience any side effect, you can report it to the MHRA via the Yellow Card scheme at https://yellowcard.mhra.gov.uk/.
How to check your suitability safely
The safest way to find out whether Mounjaro is right for you is a proper clinical review. Our free online consultation asks about your medical history, medicines and the conditions listed above, and a GPhC-registered prescriber reviews your answers. If anything needs clarifying, a short video consultation may follow.
Medicines are dispensed by our own UK pharmacy and are genuine, MHRA-licensed products. You can learn more about The Weight Clinic or contact us with questions.
This article is for information only and is not a substitute for personalised medical advice. Weight-loss medicines are prescription-only, are not suitable for everyone, and are prescribed only after a clinical consultation with a GPhC-registered prescriber. Individual results vary. Always speak to a UK-registered pharmacist or doctor before starting or changing any prescription medication.
