Senna

What is senna?

Senna is a natural stimulant laxative used to treat constipation. It’s made from the senna plant’s leaves and fruit, and is available as tablets or syrup. It can be prescribed, or purchased over the counter from pharmacies or general shops, commonly under the brand name Senokot. It’s mainly used for short-term relief of constipation[1].  

What is senna used to treat?

Senna is primarily used to: 

• Relieve occasional constipation 

• Help empty the bowels before medical examinations like a colonoscopy 

How does senna work?

Senna stimulates the muscles in your bowel, helping stool move through your intestines. It usually causes a bowel movement within 8 to 12 hours after taking it[1]. 

Who can take senna?

Senna can be used by adults aged 18 and over. Children over 12 years can take it if a doctor or pharmacist says it’s okay, while children aged 11 and under need a doctor’s prescription to take it[1]. 

Senna is not suitable for people who: 

• Have intestinal obstruction, Crohn’s disease, ulcerative colitis, or appendicitis 

• Have kidney or heart problems 

• Are allergic to senna 

• Have severe stomach pain, nausea, or vomiting 

• Have signs of dehydration or electrolyte imbalance 

• Are pregnant, trying to get pregnant, or are breastfeeding 

• Have long-term constipation. 

Please tell your doctor or pharmacist about any conditions you may have or medication you take before you start treatment, and always follow the instructions in the Patient Information Leaflet[2].  

What is the typical dose of senna and how do you take it?

For shop-bought senna tablets and syrup, the usual dose is[1]: 

• 1 or 2 tablets (7.5mg or 15mg) at bedtime (or 1 tablet of Senokot Max Strength) 

• 1 or 2 5ml spoonfuls (7.5mg or 15mg) of syrup at bedtime 

If it’s your first time taking senna, start with one 7.5mg tablet or one 5ml spoonful of syrup, and if that doesn’t work, you can then double the dose. For children aged 12 to 17 only give senna bought over the counter after discussion with a doctor or pharmacist[1].  

For prescribed senna tablets, the usual dose is[1]: 

• adults aged 18 years and over – two 7.5mg tablets, taken once a day at bedtime 

• children aged 6 to 17 years – one 7.5mg tablet, taken once a day at bedtime 

For prescribed senna syrup, the usual dose is[1]: 

• adults aged 18 years and over – one or two 5ml spoonfuls (7.5mg or 15mg) at bedtime 

• children aged 4 to 17 years – 2.5ml (half a 5ml spoonful) to two 5ml spoonfuls at bedtime 

• children aged 1 month to 3 years – 2.5ml (half a 5ml spoonful) 

A doctor may prescribe higher doses for adults and children if necessary. Please follow the instructions on your prescription or medication label[2]. 

Swallow tablets whole with water, and it can be taken with or without food. It’s best taken on an empty stomach for faster effect. It usually takes about 8 hours to work. Drink plenty of fluids or your constipation may get worse[1]. 

Can you stop taking senna?

Yes. It’s for short-term use only. Stop if constipation improves. Long-term use can cause dependency and bowel problems[1]. 

What do you do if you take too much senna?

Taking too much senna can cause[1]: 

• Severe diarrhoea 

• Dehydration 

• Abdominal cramps 

If this happens, stop taking senna and drink plenty of fluids. Contact a doctor or call NHS 111 if symptoms are severe. 

What do you do if you forget a dose of senna?

If you forget to take senna, skip the missed dose and take the next dose the following evening. Do not double up to make up for a missed dose[1]. 

Medicines you can and can’t take with senna

You should avoid the following as they can increase the risk of electrolyte imbalance[1]: 

• Diuretics (water tablets) 

• Steroids 

• Licorice root 

• Digoxin 

• Other laxatives 

Always inform your doctor or pharmacist about all medications and supplements you take before you start a new medicine, and follow the instructions in the Patient Information Leaflet[2]. 

What are the side effects of senna?

The most common side effects include[1]: 

• Stomach cramps 

• Diarrhoea 

• Nausea 

• Urine discoloration (harmless) 

Less common but serious side effects include[1]: 

• Electrolyte imbalance (more likely with long-term use) 

• Allergic reactions (rash, itching) 

Stop taking senna and seek medical help if you have severe abdominal pain, persistent diarrhoea, or an allergic reaction. 

You should contact your GP if you experience any of these symptoms. In rare cases, the medicine may cause a serious allergic reaction (anaphylaxis). You should call 999 or visit A&E immediately if you believe this is happening[1]. 

Symptoms of anaphylaxis include:

• Difficulty breathing

• Tightness in throat and chest

• Swelling of the tongue or throat

• Feeling faint or dizzy

• Blue/grey skin or lips

If you experience any side effects, including those not listed, you are encouraged to report them via the Yellow Card Scheme or contact your doctor, pharmacist, or nurse. This information is intended as a summary for general awareness and does not replace professional medical advice. 

The information provided in the side effects section is not a comprehensive list of all possible side effects associated with this medication. For a complete list of side effects, please refer to the Patient Information Leaflet (PIL) provided with your medication or consult your healthcare professional[2]. 

Frequently asked questions about senna

How long does senna take to work? 
It usually takes effect within 8 to 12 hours[1]. 

Can I take senna every day? 
No. It’s meant for short-term use only unless prescribed otherwise by your doctor[1]. 

Is senna safe during pregnancy? 
During pregnancy it is advised to treat constipation initially with lifestyle changes like increasing fibre and fluid intake, and doing gentle exercise. If these measures do not help, then a doctor or midwife may recommend a laxative. Other types of laxatives are preferred to senna in pregnancy, as there is more safety information about them[1]. 

Can I drive after taking senna? 
Yes, it doesn’t affect your ability to drive[1]. 

Can I take senna with food? 
Yes, but it usually works faster on an empty stomach. Limiting processed foods such as cakes and pastries, as well as things like cheese can help as these foods can worsen constipation. Increasing fluid and fibre in your diet will help to ease constipation[1]. 

For the official NHS guide for senna, visit their website.