Senna (Senokot): stimulant laxative explained

Senna is a plant-derived stimulant laxative. Where an osmotic laxative holds water in the stool, senna acts on the gut wall itself, triggering the bowel muscles to contract and push stool out. The NHS describes it as a treatment for constipation, for example infrequent bowel movements or dry, hard stools.

It is available as tablets and as a syrup, and the commonly named brand is Senokot. Adults and children aged 12 and over can buy it in shops and pharmacies; younger children need a doctor's prescription.

Senna takes around 8 to 12 hours to work, so it is usually taken once a day in the evening before bed, which suits a bowel movement the next morning. The NHS suggests starting at the lowest dose and increasing gradually if it does not work, and a pharmacist can tell you the amount for the product you have.

Tablets are swallowed whole with water, and the syrup is measured with the spoon or cup supplied.

• Do not take it for more than 7 days unless a doctor or pharmacist says so.

• See a doctor if there is no improvement after 3 days.

• If you miss a dose, skip it and keep to your usual schedule. Never double up.

• Extra senna is unlikely to cause problems, but ask a pharmacist or call NHS 111 if you have vomiting, diarrhoea, stomach pain, dizziness or weakness.

Most adults and children aged 12 and over can take senna. You should not use it if you have had an allergic reaction or serious side effect from senna or another laxative, if you have a bowel blockage that is not due to constipation, or if you have kidney or heart problems. The NHS also lists irritable bowel syndrome, diverticular disease and Crohn's disease as conditions to discuss first.

Tell your pharmacist if you use heart medicines for heart failure or rhythm problems, diuretics (water tablets), steroids, or anything containing liquorice root. These can interact with senna through potassium levels.

Stomach pain, cramps and discomfort and diarrhoea are the usual effects. Yellow-brown or red-brown urine can also occur; it is harmless and clears once you stop. Speak to a pharmacist or doctor if effects bother you or persist.

Serious effects are uncommon: allergic reaction (call 999 for swelling of the throat or tongue, an itchy rash or breathing difficulty), low potassium from prolonged use (muscle weakness, tiredness, passing urine often, heart problems), and muscle spasms or swollen joints. Contact NHS 111 for these or if you took more than advised on purpose.

Suspected side effects can be reported to the Yellow Card scheme.

You can usually take senna when pregnant, but speak to a pharmacist or doctor first, who may suggest diet and lifestyle changes or another laxative before senna. You can take it while breastfeeding if your baby is 1 month or older; side effects in babies are uncommon. The NHS pages do not address fertility.

Senna does not usually affect driving, cycling or using machinery. You can mostly eat and drink as normal, but avoid products made with liquorice root, such as liquorice tea and supplements, because they can add to potassium loss.

The NHS pages do not comment on alcohol with senna, so follow the leaflet in your pack.

Using stimulant laxatives for long stretches can make the bowel dependent and unbalance body salts, which is why senna has a short-use limit. Bulk-forming and osmotic laxatives such as ispaghula husk, lactulose and macrogol are alternatives, and bisacodyl is another stimulant. If constipation keeps returning, ask a pharmacist or doctor to look at the cause.