Diarrhoea is a very common side effect of weight loss medications, affecting more than 1 in 10 people taking Mounjaro® or Wegovy®. You are most likely to experience this when you first start your treatment or when you increase your dose.
Use this guide to:
Learn how to manage mild diarrhoea at home.
Understand the risks of dehydration.
Understand the updated guidance regarding oral contraception.
Identify when you need to seek urgent medical attention.
How to Manage Diarrhoea
Most cases are mild and temporary. To manage this side effect while taking Mounjaro® or Wegovy®, we recommend the following:
Stay hydrated: Drink plenty of fluids, such as water and herbal teas, to replace lost moisture.
Replenish electrolytes: Consider using oral rehydration salts (available at most pharmacies) to replace lost fluids and essential minerals.
Adjust eating habits: Eat small, frequent, bland meals rather than a few large ones to avoid taxing your digestive system.
Rest: Take it easy and allow your body time to recover.
Pain relief: You may take paracetamol if you are experiencing associated aches or mild discomfort.
Important Guidance: Weight Loss Medication and Contraception
Recent medical guidance highlights that weight loss injectables can impact the effectiveness of oral contraceptive pills.
Tirzepatide (Mounjaro®)
Clinical evidence suggests that Mounjaro® may reduce the absorption of oral contraceptive pills. To ensure you remain protected against pregnancy:
Use barrier methods: Use a barrier method of contraception (such as condoms) in addition to your pill for four weeks after starting the medication and for four weeks after every dose increase.
Consider non-oral options: Alternatively, discuss switching to a non-oral form of contraception (such as the coil, implant, or patch) with your GP, as these are not affected by weight loss injectables.
Semaglutide (Wegovy®)
Currently, there is no evidence that semaglutide reduces the effectiveness of the oral contraceptive pill. However, for all patients using GLP-1 medications, effective contraception is essential, as these drugs are not recommended during pregnancy.
If You Experience Diarrhoea
Diarrhoea lasting for more than 24 hours can interfere with the absorption of any oral medication, including the contraceptive pill. If your diarrhoea is prolonged, the medication may not have been fully absorbed. In these instances, follow the standard guidance for a "missed pill" and use additional barrier protection (such as condoms) until your symptoms resolve.
When to Contact Your GP or Call 111
Contact a healthcare professional if you experience any of the following:
Diarrhoea that lasts for more than one week.
Blood in your stool.
Signs of dehydration, such as passing dark urine or urinating less frequently than usual.
(Always inform the healthcare provider that you are taking weight loss medication.)
When to Seek Urgent Medical Help
Call 999 or go to your nearest A&E immediately if your diarrhoea is accompanied by:
Sudden or severe stomach pain.
High fever or chills.
(Ensure you disclose that you are taking Mounjaro® or Wegovy® to emergency services.)
Additional Resources
For further information on managing side effects and general guidance on GLP-1 weight loss treatments, visit our Weight Loss Health Guide.
If you still need help after reviewing the information above, additional assistance is available from the MedExpress team.