Like all medicines, senna may cause side effects in some people, but many people have no side effects or only minor ones.
Common side effects
Common side effects of senna, which happen in more than 1 in 100 people, are stomach cramps and diarrhoea.
You are particularly likely to get stomach cramps and diarrhoea with senna if you have constipation related to irritable bowel syndrome (IBS).
Stop taking senna if you get diarrhoea.
If you take the combined contraceptive 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.
Your pee may turn a red-brown colour while you’re taking senna. This is harmless and returns to normal after treatment has ended.
Talk to your doctor or pharmacist if the side effects bother you or do not go away.
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to senna.
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.
Long-term side effects
Ideally you'll only take senna for a few days. Taking it for a long time can cause an electrolyte imbalance, where levels of substances like sodium, potassium and magnesium in your body get too high or too low.
A severe electrolyte imbalance can cause serious health problems, such as muscle spasms or twitching, and even cause a seizure or fit.
Using senna for many weeks, even months, could also stop your bowel working properly on its own.
Only take senna regularly long term if it has been prescribed for you.
Other side effects
These are not all the side effects of senna. 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.