Like all medicines, mebendazole can cause side effects, although not everyone gets them.
Common side effects
These common side effects of mebendazole happen in more than 1 in 100 people. There are things you can do to help cope with them:
Stomach pain
Try to rest. It can help to eat and drink slowly and have smaller and more frequent meals. Placing a heat pad or covered hot water bottle on your stomach may also help.
If you're in a lot of pain, speak to a doctor or pharmacist.
Stomach discomfort including bloating and wind
Stick to simple meals and avoid rich or spicy food. It might help to take mebendazole after you've eaten to see if that helps ease the symptoms.
Diarrhoea
Drink plenty of water or other fluids to avoid dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee.
Do not take any other medicines to treat diarrhoea without speaking to a pharmacist or doctor first.
If you take the combined pill or progestogen-only pill and you have severe diarrhoea for more than 24 hours, your contraception may not protect you from pregnancy. Check the pill packet to find out what to do.
Speak to a doctor or pharmacist if the advice on how to cope does not help and a side effect is still bothering you or does not go away.
Serious side effects
Stop taking mebendazole and call a doctor or call 111 straight away if the whites of your eyes turn yellow, or your skin turns yellow although this may be less obvious on brown or black skin. These can be signs of liver problems.
Immediate action required: Call 999 or go to A&E if:
- you or your child has a fit or seizure
Do not drive to A&E. Ask someone to drive you or call 999 and ask for an ambulance.
Bring all the medicines you take with you.
Serious allergic reaction
It happens rarely but it's possible to have a serious allergic reaction (anaphylaxis) to mebendazole.
Immediate action required: Call 999 now if:
- your lips, mouth, throat or tongue suddenly become swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- your throat feels tight or you're struggling to swallow
- your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
- you suddenly become very confused, drowsy or dizzy
- someone faints and cannot be woken up
- a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)
You or the person who's unwell may also have a rash that's swollen, raised, itchy, blistered or peeling.
These can be signs of a serious allergic reaction and may need immediate treatment in hospital.
Do not drive yourself to A&E.
The person you speak to at 999 will give you advice about what to do.
Other side effects
These are not all the side effects of mebendazole. For a full list see the leaflet inside your medicines packet.
Reporting side effects
You can report any suspected side effect using the Yellow Card safety scheme.
Visit the Yellow Card website for more information about reporting side effects.