1. About senna
Senna is a natural laxative made from the leaves and fruit of the senna plant. It's used to treat constipation (difficulty pooing).
Senna comes as tablets and as a liquid that you swallow (syrup).
It's available on prescription and to buy from pharmacies. Small packs are available to buy from supermarkets (up to 20 standard strength tablets, 10 maximum strength tablets or 100ml of syrup).
It's also combined with other ingredients in constipation remedies such as Manevac and Senokot Dual Relief tablets.
Before trying senna, it’s better to try other ways to help your constipation by:
- having more fibre in your diet
- drinking more water and exercising
Only use senna if you have tried other types of laxatives first such as:
2. Key facts
- 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 1 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.
3. Who can and cannot take senna
Senna is safe to take for most adults aged 18 years and over.
It can only be used by children (aged 17 years or younger) if a doctor or pharmacist recommends it.
Only give senna to children if a doctor or pharmacist recommends it.
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:
4. How and when to take it
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 years and over is 1 or 2 tablets at bedtime (or 1 tablet of Senokot Max Strength)
- children aged between 6 and 11 years is 1 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 do not 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, do not worry, just take the next dose the following evening.
Never take 2 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 is unlikely to harm you.
You may get stomach pain and diarrhoea but this should ease off within 1 or 2 days.
If you're worried, talk to your doctor or a pharmacist.
5. Side effects
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.
Talk to your doctor or pharmacist if the side effects bother you or do not go away.
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.
If you get a severe skin rash, stop taking senna and call your doctor straight away.
Serious allergic reaction
In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to senna.
Immediate action required: Call 999 or go to A&E now if:
- you get a skin rash that may include itchy, red, swollen, blistered or peeling skin
- you're wheezing
- you get tightness in the chest or throat
- you have trouble breathing or talking
- your mouth, face, lips, tongue or throat start swelling
You could be having a serious allergic reaction and may need immediate treatment in hospital.
These are not all the side effects of senna. For a full list see the leaflet inside your medicines packet.
You can report any suspected side effect using the Yellow Card safety scheme.
6. How to cope with side effects of senna
What to do about:
- diarrhoea – you may need to stop taking senna or reduce your dose. Until the diarrhoea stops, 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. Reducing your dose of senna may also help diarrhoea. Do not take any other medicines to treat diarrhoea without speaking to a pharmacist or doctor.
- stomach cramps – try to rest and relax. It can help to eat and drink slowly and have smaller and more frequent meals. Putting a heat pad or covered hot water bottle on your stomach may also help. If the cramps do not get better, try reducing your dose of senna. If you are in a lot of pain, speak to your pharmacist or doctor.
7. Pregnancy and breastfeeding
Senna may not be suitable if you're pregnant or 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 do not work, you may be recommended a laxative. Laxatives are usually safe for pregnant women to take because most of them are not absorbed by the digestive system. This means that your baby will not feel the effects of the laxative.
However senna is partly absorbed by your gut. Your doctor or midwife will usually only recommend senna if other laxatives have not worked.
Non-urgent advice: Tell your doctor if you're:
- trying to get pregnant
For more information about how senna can affect you and your baby during pregnancy, read this leaflet on treating constipation on the Best Use of Medicines in Pregnancy (BUMPs) website.
8. 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 (tablets which make you pee more)
- steroid tablets
- liquorice root preparations
Mixing senna with herbal remedies and supplements
Apart from liquorice root preparations, there are no known problems with taking other herbal remedies and supplements with senna.
Important: Medicine safety
Tell your doctor or pharmacist if you're taking any other medicines, including herbal medicines, vitamins or supplements.
9. Common questions about senna
How does senna work?
Senna is known as a stimulant laxative – it stimulates the muscles that line your gut, helping them to move poo along your bowel.
When will I feel better?
Senna takes about 8 hours to work.
Talk to your doctor if you are still constipated after 3 days.
How long will I take senna for?
Take senna for a few days only and certainly no longer than a week. If you take senna for longer, your body can start to rely on it, rather than your bowels doing the work on their own.
If you are still constipated after taking senna for 3 days, talk to your doctor.
Is it safe to take senna for a long time?
Ideally, you should only use senna occasionally and for a few days at a time.
Using senna for longer can lead to diarrhoea. Stop taking it if you get diarrhoea.
It can also 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 spasm and twitching, and even convulsions.
Using senna for many weeks, even months, could also stop your bowel working properly on its own.
Can I take different laxatives together?
For most people, 1 laxative will be enough to relieve constipation.
Occasionally, you may need to take 2 different types of laxatives at the same time to get your bowels moving again. Only take 2 laxatives together on the advice of your doctor or pharmacist as there is an increased risk of side effects.
Are other laxatives any better?
There are other types of laxatives. They work in a different way to senna but are equally good at treating constipation. Some take longer to work than senna.
- Bulk-forming laxatives, for example Fybogel and methylcellulose. These increase the "bulk" or weight of poo which in turn stimulates your bowel. These laxatives take 2 or 3 days to work.
- Osmotic laxatives, for example lactulose. These draw water from the rest of the body into your bowel to soften poo and make it easier to pass. They take at least 2 days to work.
- Surface-wetting laxatives, for example arachis oil and docusate sodium. These let water into poo to soften it and make it easier to pass.
Will it affect my fertility?
There's no clear evidence to suggest that taking senna will reduce fertility in either men or women.
However, speak to a pharmacist or your doctor before taking it if you're trying to get pregnant.
Will it affect my contraception?
If you have severe diarrhoea your contraceptive pills may not protect you from pregnancy. Look on the pill packet to find out what to do.
Is there any food or drink I need to avoid?
You can eat and drink normally with senna.
It might be a good idea to stop eating pastries, puddings, sweets, cheese and cake for a while as these foods can make constipation worse.
Can I drink alcohol with it?
Yes, you can drink alcohol with senna.
Can I take senna after surgery?
It's quite common to have constipation after surgery. Using a laxative may help relieve the discomfort.
If you have constipation after an operation, it's better to use lactulose because it's gentler on your stomach muscles than senna.
Can lifestyle changes help constipation?
It's often possible to relieve constipation without having to use laxatives. Before trying senna – or to stop constipation coming back – it may help to:
- get more fibre into your diet – aim for about 30g of fibre a day. High-fibre foods include fruit, vegetables and cereals. If you are not used to a high-fibre diet, it may be best to increase the amount of fibre you eat gradually
- add bulking agents, such as wheat bran, to your diet. These will help make your poo softer and easier to pass (although bran and fibre can sometimes make bloating worse)
- drink plenty of water – to keep poo soft
- exercise – keeping your body active will help to keep your gut moving
Only use senna if you have tried other types of laxatives first such as: