Like all medicines, mirabegron can cause side effects in some people, but many people have no side effects or only minor ones.
Side effects often improve as your body gets used to the medicine.
Common side effects
These common side effects of mirabegron are usually mild and do not last long. There are things you can do to help cope with them:
Feeling sick (nausea)
Try taking mirabegron with food. It may also help if you stick to simple meals and avoid rich or spicy food.
Constipation
Get more fibre into your diet such as fresh fruit, vegetables and cereals, and drink plenty of water. Try to exercise more regularly, for example, by going for a daily walk or run. If this does not help, talk to your pharmacist or doctor.
Diarrhoea
Drink lots of fluids, such as water or squash, 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.
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 for advice.
Headache
Make sure you rest and drink plenty of fluids. Do not drink too much alcohol. Ask a pharmacist to recommend a painkiller. Talk to your doctor if the headaches continue or are getting worse.
Feeling dizzy
Stop what you're doing and sit or lie down until you feel better. Do not drive, ride a bike or operate machinery until it passes. If the dizzy spells continue, speak to your doctor.
Fast heart rate
Mirabegron can cause a fast heart rate where you can feel your heart beating faster than usual for no obvious reason (like vigorous exercise).
Lie down and try to relax. This is usually nothing to worry about and will pass. Call 111 if your heartbeat does not slow down after resting.
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
Serious side effects are rare and happen in less than 1 in 1,000 people.
Call a doctor or call 111 for advice now if:
- you have problems emptying your bladder completely, or problems starting to pee
- you have pain or a burning sensation when you pee, or smelly or cloudy pee – these could be signs of a urinary tract infection (UTI)
- you have irritated eyes and red or swollen eyelids
- you get small spots on your skin that are purple but not itchy
- you get a fast heartbeat that does not slow down after resting
Immediate action required: Call 999 or go to A&E if:
- you have chest pain
- you have a very severe headache
- you have difficulty breathing
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
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to mirabegron.
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 mirabegron. 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.