Senna is a natural laxative made from the leaves and fruit of the senna plant. It is used to treat constipation (difficulty pooing).
Senna comes as tablets and as a liquid that you swallow.
It is available on prescription and to buy from pharmacies and supermarkets.
It is also combined with other ingredients in constipation remedies such as Manevac and Senokot Dual Relief tablets.
- Senna takes about 8 hours to work.
- It's best to take senna at bedtime so it works overnight.
- The most common side effects are stomach cramps and diarrhoea. These are usually mild and short-lived.
- Do not take senna for more than a week. Long term use of senna can stop your bowel working properly on its own.
- Pee may turn a red-brown colour while you take senna. This is harmless and returns to normal after treatment has finished.
Who can take senna
Senna is safe to take for most adults.
Do not give senna to a child under 6 unless your doctor has said it's ok.
Senna may not be suitable for everyone. To make sure senna is safe for you, tell your doctor or pharmacist before starting senna if you have:
How and when to take
Take senna once a day at bedtime. You can take senna with or without food.
The normal dose of senna tablets for constipation in:
- adults and children aged 12 and over is 1 or 2 tablets at bedtime
- children aged between 6 and 11 is a single tablet at bedtime
The normal dose of senna syrup for constipation in:
- adults and children aged 6 years and over is one or two 5ml spoonfuls at bedtime
- children aged 2 to 5 years (only under medical supervision) is half to one 5ml spoonful at bedtime
Liquid senna comes with a plastic cup or spoon to measure the dose. Do not use a kitchen spoon as it will not give the right amount. If you don't have a cup or spoon, ask your pharmacist for one.
Senna takes about 8 hours to work. It's normal to take it at bedtime so it works overnight.
Drink plenty of fluids (6 to 8 glasses a day) while you are taking senna or your constipation may get worse.
What if I forget to take it?
If you forget a dose of senna, don't worry, just take the next dose the following evening.
Never take two doses at the same time. Never take an extra dose to make up for a forgotten one.
What if I take too much?
Taking an extra dose of senna by accident is unlikely to harm you.
You may get stomach pain and diarrhoea but this should ease off within a day or two.
If you are worried, talk to your doctor or pharmacist.
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, 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.
Your pee may turn a red-brown colour while you are taking senna. This is normal and returns to normal after treatment has ended.
If any side effects carry on, or if you are worried, talk to your doctor or pharmacist.
Serious side effects
A very rare but serious side effect of senna is a severe raised, red, itchy skin rash on any part or all of your body. This happens in less than 1 in 10,000 people.
If you get a severe skin rash, stop taking senna and tell your doctor straight away.
Serious allergic reaction
The warning signs of a serious allergic reaction are:
- getting a skin rash that may include itchy, red, swollen, blistered or peeling skin
- tightness in the chest or throat
- having trouble breathing or talking
- swelling of the mouth, face, lips, tongue or throat
A serious allergic reaction is an emergency. Contact a doctor straight away if you think you or someone around you is having a serious allergic reaction.
How to cope with side effects
What to do about:
- diarrhoea – drink plenty of water or other fluids. It may also help to take oral rehydration solutions. You can buy these from a pharmacy to prevent dehydration. Reducing the dose of senna may also help diarrhoea. Don’t take any other medicines to treat diarrhoea without speaking to a pharmacist or doctor
- stomach cramps – if you get stomach cramps, reduce your dose of senna until it goes away
Pregnancy and breastfeeding
Constipation is common at the end of pregnancy and just after having a baby.
If you're pregnant or breastfeeding, it's better to ease constipation without taking a medicine. Your doctor or midwife will first advise that you eat more fibre and drink plenty of liquids. You'll also be encouraged to do gentle exercise.
If dietary and lifestyle changes don't work, you may be recommended a laxative.
Laxatives are usually safe for pregnant women to take because most of them aren't absorbed by the digestive system. This means that your baby won't feel the effects of the laxative.
Senna may not be suitable if you're pregnant or breastfeeding because it's partly absorbed by your gut.
Cautions with other medicines
There are some medicines that do not mix well with senna and can change the way it works.
Tell your doctor if you are taking these medicines before starting senna:
- a heart medicine such as digoxin or quinidine
- a diuretic (water tablet)
- steroid tablets
- liquorice root preparations
Mixing senna with herbal remedies and supplements
There are no known problems with taking herbal remedies and supplements with senna.
However, for safety, speak to your pharmacist or doctor before taking senna if you routinely take any herbal or alternative remedies.
How does Senna work?
When will I feel better?
How long will I take senna for?
Is it safe to take senna for a long time?
Can I take different laxatives together?
Are other laxatives any better?
Is there any food or drink I need to avoid?
Can I take senna after surgery?
Can I drink alcohol with it?
Can lifestyle changes help constipation?