Who Should Not Take Mounjaro or Wegovy? A GP's Guide

Wegovy (semaglutide) and Mounjaro (tirzepatide) are new weight-loss medicines that can help some people lower their risk of type 2 diabetes, joint pain, and heart disease. A lot of people ask me if these weight-loss injections are right for them, and while they can offer real benefits, they aren't suitable for everyone. Here's a quick guide to who should avoid these medicines, and who needs extra caution.

Who should not take these medications?

There are certain people who are not advised to take either Mounjaro or Wegovy at all. You should not take Mounjaro or Wegovy if you have any of the following:

1. Personal or family history of medullary thyroid carcinoma or MEN2: These medicines carry a warning for a rare thyroid cancer called medullary thyroid carcinoma (MTC) and a related condition, Multiple Endocrine Neoplasia type 2 (MEN2) (NICE TA1026/TA875, BNF). If you or a close family member has either of these, these medicines should not be prescribed.
2. Allergy to the active ingredient: If you are allergic to tirzepatide (Mounjaro) or semaglutide (Wegovy), or have reacted to any GLP-1 medicine before, you should not take them (MHRA, BNF). Tell your prescriber about any allergies before starting.
3. Breastfeeding and Pregnancy: Neither medicine is considered safe during pregnancy or breastfeeding. Both should be stopped before trying to conceive. Your prescriber should discuss contraception options with you, as losing weight can also affect fertility.
4. History of pancreatitis: These medicines have been linked to pancreatitis (BNF, MHRA). If you have had pancreatitis, you should not use them.
5. Less than 18 years of age: Neither of these medications is currently licensed for use in adolescents or children in the UK (NICE TA1026/TA875, BNF).

Who should use these medicines with caution?

Some people may be able to use these medicines, but will need extra care and regular check-ins with their healthcare team. Caution is needed if you have:

1. Severe gastrointestinal conditions: These two medicines work by slowing the rate at which we empty food from the stomach. This, therefore, can lead to worsening of conditions such as severe gastro-oesophageal reflux or Gastroparesis (delayed stomach emptying).
2. Liver or kidney disease: Significant liver or kidney problems may require closer monitoring or dose adjustments (BNF, MHRA). Your prescriber will check your liver and kidney function first.
3. History of eating disorders: Let your doctor know if you have ever had an eating disorder, as these medicines affect appetite and need careful support (NICE, BNF).
4. Diabetic eye disease: Rapid improvement in blood sugar, especially with Wegovy, can worsen diabetic eye disease in the short term (MHRA, NICE TA1028). Tell your prescriber if you have diabetic retinopathy.
5. Taking insulin or sulphonylureas: These medicines can lower blood sugar further, so your doses may need adjusting (MHRA, BNF). Make sure your diabetes team and prescriber are aware of all your treatments.

Concerning / red flag symptoms: when to seek medical help

If you have already started Mounjaro or Wegovy and happen to notice any of the following, you need to seek urgent medical attention:

• Severe or persistent abdominal pain, and in particular a pain that spreads to the back, as this could indicate pancreatitis
• Swelling of the face, lips or throat, difficulty breathing or a widespread rash are signs of an allergic reaction.
• Swelling or a lump in the neck, trouble swallowing, or hoarseness could be thyroid issues and should be checked promptly.
• Any sudden vision changes should be reviewed promptly if you have diabetes.

What should a good prescriber do before starting treatment?

Before prescribing, your doctor should review your medical and family history, check your current medications, and arrange blood tests (liver, kidney, and blood sugar). They should ensure you meet the criteria, explain how to take the medication, discuss possible side effects, and tell you when to seek help.

If you have been offered either Wegovy or Mounjaro and you have not received a proper consultation or any questions you have about your suitability for these medicines have not been fully addressed, it is worth seeking a more thorough review before stating.

This article is for general information only and does not constitute personal medical advice. Always speak to a qualified, GMC-registered clinician before starting any prescription medicine.

Related weight-loss guides

• Mounjaro patient information — UK patient information on tirzepatide
• Mounjaro vs Wegovy — mechanism, efficacy and side effects compared
• Mounjaro and Wegovy side effects — patient-reported effects and safety data
• How to get Mounjaro in the UK — eligibility and prescriber checks
• NHS weight-loss medication eligibility — whether NHS-funded access is realistic