Senna can take 8-12 hours to have an effect. It is best taken in the evening.
If you are still constipated after taking senna for three days, make an appointment to speak with your doctor.
Eating a healthy diet, drinking plenty of water and getting regular gentle exercise can all help prevent constipation.
|Type of medicine||A stimulant laxative|
|Also called||Senokot®; Potter's Senna®|
|Available as||Tablets and oral liquid medicine|
Constipation is a common problem. It can mean either going to the toilet less often than usual to empty your bowels, or passing hard or painful stools. Constipation can be caused by a number of things. Not eating enough fibre or not drinking enough fluid can cause constipation. Some conditions (such as pregnancy) can cause constipation, as can a lack of exercise or movement (such as being ill in bed) and some medicines.
Often, increasing the amount of fibre in your diet (such as by eating more fruit, vegetables, cereals, and wholemeal bread) and drinking plenty of water each day can effectively prevent or relieve constipation.
You could be recommended senna as a laxative to help relieve constipation if you cannot increase the fibre in your diet, or if this is insufficient. Senna works by encouraging the muscles in your bowel to move stools through your body. This helps you to go to the toilet. It usually has an effect within 8-12 hours. It is available to buy without a prescription at pharmacies and other retail outlets.
Before taking senna
To make sure that this is the right treatment for you, before you start taking senna it is important that you speak with your doctor or a pharmacist if:
- You are pregnant or breastfeeding. This is because, if you are expecting a baby or breastfeeding, medicines should only be taken on the advice of a doctor or nurse.
- It is intended for a child. Laxatives should only be given to children on the advice of a doctor, or a healthcare professional experienced in the management of constipation in children.
- You are so constipated that you think you may have a blockage.
- You are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.
- You have ever had an allergic reaction to a medicine.
How to take senna
- Before taking senna, read the manufacturer's printed information leaflet from the pack. It will give you more information about the medicine and will provide you with a full list of the side-effects which you could experience.
- The usual adult dose is two to four tablets, or two to four 5 ml spoonfuls (10-20 ml) of liquid medicine once a day. Take senna in the evening. It should only be used for a few days - this is because your bowel can start to rely on this type of laxative to make it work rather than working on its own. If you are still constipated after taking senna for three days, you should make an appointment to speak with your doctor.
- If a doctor or healthcare professional has recommended senna for your child, check the label on the pack carefully to make sure that you give the correct dose for the age of your child.
Getting the most from your treatment
- It is important for you to drink plenty while you are constipated. Adults should aim to drink at least two litres (about 8-10 cups) of fluid per day. Most sorts of drink will do but, as a start, try just drinking a glass of water 3-4 times a day in addition to what you normally drink.
- Try to eat a balanced diet containing high-fibre foods such as wholemeal and wholegrain breads and cereals, fruit and vegetables, brown rice and wholemeal pasta. If you are not used to a high-fibre diet, it may be best to increase the amount of fibre you eat gradually.
- Keeping your body active will help you to keep your digestive system moving, so try to take some regular daily exercise.
- You may wish to include some foods in your diet that contain sorbitol. Sorbitol is a naturally occurring sugar. It is not digested very well and draws water into your bowel which has an effect of softening stools. Fruits (and their juices) which have a high sorbitol content include apples, apricots, gooseberries, grapes (and raisins), peaches, pears, plums, prunes, raspberries and strawberries.
- Food such as pastries, puddings, sweets, cheese and cake can make constipation worse and are probably best avoided.
- You can read more about how to prevent or treat constipation in the separate condition leaflets called Constipation in Adults and Constipation in Children.
Can senna cause problems?
Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the ones which can occur with senna. You will find a full list in the manufacturer's information leaflet supplied with your medicine. Speak with your doctor or pharmacist if any of the following continue or become troublesome.
|Side-effects of senna||What can I do if I experience this?|
|Stomach pain or cramp, diarrhoea||Stop taking senna|
If you experience any other symptoms which you think may be due to senna, please speak with your doctor or pharmacist for further advice.
How to store senna
- Keep all medicines out of the reach and sight of children.
- Store in a cool, dry place, away from direct heat and light.
Important information about all medicines
If you buy any medicines check with a pharmacist that they are safe to take with your other medicines.
Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.
If you are having an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.
Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy who will dispose of them for you.
If you have any questions about this medicine ask your pharmacist.
Further reading and references
Manufacturer's PIL, Senokot® Tablets; Forum Health Products Ltd, The electronic medicines Compendium. Dated February 2016.
Manufacturer's PIL, Senokot® Syrup; Forum Health Products Limited, The electronic Medicines Compendium. Dated February 2016.
British National Formulary, 76th Edition (Sep 2018); British Medical Association and Royal Pharmaceutical Society of Great Britain, London.