A stimulant laxative for constipation
Senna
A stimulant laxative that encourages the bowel to move, used for short-term relief of constipation.
What is Senna?
Senna (Senokot) is a stimulant laxative. It works on the bowel wall to encourage a bowel movement, and is used for the short-term relief of constipation. It usually works overnight, so it is often taken before bed.
Education and reference only. This is a plain-language guide to Senna — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Senna is a stimulant laxative made from a plant extract and used to relieve constipation. In the UK it is one of the most familiar laxatives, available on prescription and to buy from pharmacies and shops. It is generally used for short-term relief, or sometimes longer-term where constipation is an ongoing problem, such as with certain medicines.
How it works
Senna stimulates the nerves and muscle in the wall of the large bowel, encouraging the bowel to contract and move its contents along. It also increases the amount of fluid in the bowel, which softens the stool and helps it pass. Because of this it usually produces a bowel movement after several hours.
Company & origin
Originated / developed by: Originally derived from senna plant extracts.
A long-established, plant-derived stimulant laxative widely used in the UK.
Practical use
How to take Senna
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it by mouth with a drink of water, usually in the evening so it works by the next morning.
- Drink plenty of fluids and keep up your fibre intake while using it.
- Use it for short-term relief unless a clinician has advised longer-term use.
- Stop and seek advice if you get severe tummy pain, or if constipation does not improve.
- If you miss a dose, simply take the next one as planned — do not take extra to catch up.
Weighing it up
Advantages & disadvantages of Senna
Advantages
- Reliably relieves short-term constipation, usually working overnight.
- Widely available, inexpensive and easy to use.
- Can be combined with fluid and fibre measures for everyday constipation.
Disadvantages
- Can cause cramping tummy pain and a sudden urge to go.
- Long-term daily use without advice can make the bowel rely on it.
- Not suitable when constipation is caused by a blockage in the bowel.
Practical use
Good to know
Senna typically works overnight, so it is often taken in the evening to give a bowel movement the next morning. It is best used for short periods alongside drinking plenty of fluids and eating enough fibre. Using strong stimulant laxatives every day for a long time without advice is not recommended, as the bowel can become reliant on them. It can cause cramping tummy pain, and the urine may temporarily look slightly discoloured, which is harmless.
Who should not take it / use with caution
- People with a suspected or known bowel obstruction, or severe ongoing tummy pain of unknown cause.
- People with inflammatory bowel conditions in a severe flare, unless advised by a clinician.
- Check suitability in pregnancy and breastfeeding, and seek advice for children, before using it.
Monitoring
- Whether bowel movements return to normal and constipation eases.
- Tummy cramps or diarrhoea suggesting the dose is too high.
- With prolonged use, the need to review long-term laxative use with a clinician.
Side effects
- Cramping or colicky tummy pain.
- Diarrhoea if the dose is more than needed.
- Temporary harmless discolouration of the urine; rarely, with prolonged use, low potassium levels.
Key interactions
- Overuse can lower potassium, which may matter with medicines such as digoxin or water tablets (diuretics).
- Other laxatives taken together can increase the risk of diarrhoea and cramping.
- Tell your pharmacist about your other medicines, especially heart medicines, before regular use.
Available as: Tablets and an oral liquid or syrup; also available combined with a stool softener.
Answers
Senna: frequently asked questions
How long does senna take to work?
Senna usually produces a bowel movement after several hours, which is why it is often taken in the evening to work by the next morning.
Can I take senna every day?
It is best used for short-term relief. Taking strong stimulant laxatives daily for a long time without advice can make the bowel rely on them, so speak to a pharmacist or doctor if you need it regularly.
Why does senna cause tummy cramps?
Because it stimulates the bowel muscle to contract, it can cause cramping or colicky pain. Reducing how much you take often helps.
Is senna safe in pregnancy?
Some laxatives are used in pregnancy under advice, but check with your doctor, midwife or pharmacist first so they can recommend a suitable option.
What should I do if senna does not work?
If constipation does not improve, or you have severe tummy pain, bleeding or vomiting, stop taking it and seek advice from a pharmacist or doctor.
The wider class
About Laxatives
Senna belongs to the laxatives class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
Browse by body system
Authoritative sources
- BNF
- NICE CKS
Building a medicines information resource?
We create evidence-led, dose-free drug and formulary references for teams.