What are Senna tablets?
Senna tablets contain sennosides, a plant-derived stimulant laxative for occasional constipation. The sennosides in these tablets are supplied as calcium salts. They stimulate bowel movements and usually work overnight, within 8–12 hours.
Senna is for short-term use. The fact that it comes from a plant does not make it free of side effects; cramps and diarrhoea can occur.
Try changes to diet, fluid intake and activity, and a bulk-forming laxative where appropriate, before using senna. Seek advice if there is no bowel movement after three days or you need a laxative every day. Do not use for more than one week unless your doctor directs you to.
What can cause constipation?
Constipation is a common condition that can affect people of all ages and can be caused by lifestyle factors such as a lack of fibre in the diet, dehydration, or a sedentary lifestyle. Other causes of constipation include certain medical conditions and medications such as opioids. When left untreated, constipation can lead to discomfort, bloating.
How do Senna tablets work?
Bacteria in the large bowel break down sennosides into active compounds. These stimulate contractions that move stools through the bowel and increase the amount of water in the bowel, helping stools pass more easily.
This action explains why senna is usually taken at bedtime. Taking extra tablets before the first dose has had time to work can increase cramps and diarrhoea.
The dose of Senna 7.5mg tablets
For adults, older people and children aged 12 and over:
- Swallow one tablet at night with water to start with.
- If needed, increase to two tablets at night. Do not exceed this dose unless your doctor tells you to.
- Reduce and stop once normal bowel movements return. Taking it two or three times a week is usually enough during the short course.
Do not give to children under 12 or use for more than one week without medical advice. Contact a doctor, pharmacist or nurse if symptoms worsen, there is no bowel movement after three days, abdominal pain continues or you need a laxative every day.
How long does it take for Senna tablets to work
It can take between 8-12 hours to see a response. This is why it’s best to take them at bedtime so they can work overnight.
Who cannot take Senna tablets?
Do not take these tablets if any of the following apply. Ask a doctor or pharmacist about an alternative:
- You are under 12, pregnant or breastfeeding.
- You are allergic to sennosides or another ingredient.
- You have bowel blockage, narrowing or poor bowel muscle activity, appendicitis, Crohn’s disease or ulcerative colitis.
- You have severe dehydration, persistent or unexplained abdominal pain, nausea or vomiting.
- You have faecal impaction, unexplained rectal bleeding or blood in your stools.
- You have kidney or heart disease.
- A sudden change in bowel habit has lasted more than two weeks, or another laxative has not relieved your constipation.
Senna tablet ingredients
Active ingredient: each uncoated tablet contains sennosides as calcium salts, equivalent to 7.5mg hydroxyanthracene glycosides calculated as sennoside B.
Other ingredients: lactose monohydrate, anhydrous calcium hydrogen phosphate, maize starch and magnesium stearate. Speak to a doctor before use if you have been told that you cannot tolerate some sugars.
Side effects
Senna can cause side effects, including stomach cramps and diarrhoea. Other symptoms reported with laxatives include:
- Abdominal discomfort
- Nausea (feel sick)
- Vomiting
- Diarrhoea
Stop taking senna if you develop diarrhoea and seek advice if it continues. More serious symptoms need medical assessment:
- Severe diarrhoea or vomiting
- Feeling more tired than usual
- Shortness of breath
- Swollen ankles, feet or legs (oedema)
- Muscle weakness
- Irregular heartbeat
If you experience any of the above, contact 111 or your doctor for advice
Stop taking the tablets and get urgent medical help for difficulty breathing or swelling of the face, tongue or throat. If you take too many tablets, contact a doctor and take the pack with you.
Senna and Diarrhoea
Stop taking senna if you get diarrhoea and drink enough fluids to avoid dehydration. Speak to a pharmacist or doctor if diarrhoea continues or you feel unwell.
Frequently Asked Questions
How long does Senna take to work?
Senna can take between 8 - 12 hours to work, depending on the severity of your constipation. It is best to take senna just before you go to sleep so it can work overnight.
How long can I use Senna for?
Do not use for more than one week unless your doctor has told you to. Seek advice sooner if there is no bowel movement after three days, symptoms worsen, pain persists or you need laxatives every day.
Can Senna help with weight loss?
No, Senna is not intended for weight loss and should not be used as a weight loss aid. It will only cause you to lose weight due to water loss. However this is dangerous and not sustainable. Prolonged use of Senna can lead to dehydration, electrolyte imbalances, and other complications, which can be harmful to your health.
Can you buy Senna over the counter?
In the UK, Senna is classed as Pharmacy medicine meaning it is available to buy over the counter after a short consultation with a pharmacist.
Senna and other medicines
Ask a pharmacist to check your medicines before use, including herbal products. In particular, tell them about digoxin or other cardiac glycosides, medicines for an irregular heartbeat such as quinidine, medicines that affect the heart’s QT interval, diuretics (water tablets), corticosteroids and liquorice-root preparations. Laxative-related changes in potassium and other salts can increase the risks of some combinations.
How to store Senna tablets
Keep in the original container, out of the sight and reach of children. No special storage conditions are required. Check the expiry date and return unused medicine to a pharmacy.
