Awaiting clinical review. This entry is sourced but has not yet been signed off by a pharmacist or clinician.

Senna alexandrina (leaf, pod)

Senna

Senna works for constipation: a 2021 systematic review graded it good evidence, and it is one of only two over-the-counter laxatives to get the top recommendation. It is meant for short-term use only, because using it for more than a brief period can impair bowel function and cause dependence, and the EU regulator sets a limit of 1 week. It should not be used in pregnancy, while breastfeeding, or by children under 12.

Written by

Healthy and Herbal editorial team

Updated

29 September 2026

At a glance

Last reviewed 29 September 2026

Evidence

Moderate

Best for

Short-term constipation

Typical form & use

Extract, 10–30 mg sennosides at night

Onset

Same night

Safety

Not for over 1 week; not in pregnancy or under 12s. 4 known interactions, most serious with liquorice root.

Check with your medications →

What it's used for

Evidence is rated per use. The same ingredient can be strong for one thing and traditional for another.

Use	Evidence	What the research shows
Constipation	Moderate	A 2021 systematic review of over-the-counter laxatives found two placebo-controlled trials of senna lasting 4 weeks or more, both favouring senna on symptoms and stool frequency, and graded it good evidence (grade A). Limits: only two senna trials, sponsor funding from Bayer, and in the newer trial (starting dose 1 g a day, higher than typical US practice) 83.3% of people needed a dose reduction for abdominal pain or diarrhoea. The trials were in chronic constipation over weeks, whereas the EU licence covers occasional constipation for up to 1 week.^1,4
Bowel preparation before colonoscopy	Limited	A 2022 meta-analysis of 11 trials (3,343 patients) found senna-based regimens cleaned the bowel no better and no worse than other regimens (odds ratio 1.02, 95% CI 0.63 to 1.67). People on senna regimens tolerated them better (odds ratio 1.66) and were more likely to complete them (odds ratio 3.05). The comparison regimens varied, so this does not show how senna performs alone; it is used under medical direction.²
Constipation after childbirth	Limited	A Cochrane review found one trial (471 women) in which senna increased the number having a first bowel movement within 24 hours (risk ratio 2.90) and also increased abdominal cramps (risk ratio 4.23). Certainty was low or very low, and the review concluded there was too little evidence to draw general conclusions. The EU regulator contraindicates senna during breastfeeding, so this is a question for a midwife or doctor.^3,4

How much

Ranges below are what studies used and what supplements commonly contain. They are not a recommendation for you. Start at the low end.

EU monograph dose

10–30 mg sennosides, once at night⁴

Expressed as hydroxyanthracene derivatives calculated as sennoside B, for adolescents over 12 and adults. The right dose is the smallest that produces a comfortable soft stool.

Time to effect

8–12 hours⁴

The active compound is produced by bacteria in the large intestine, so bowel movement comes after a delay, which is why it is taken at night.

Upper limit

1 week, usually 2–3 doses⁴

The EU monograph says not to use it for more than 1 week, and that two to three doses in that week are usually enough. See a doctor or pharmacist if symptoms persist.

Dose in chronic-constipation trials

Up to 1 g a day in one trial¹

This was the starting dose in a recent trial, and most participants needed to cut it back. It is not a recommended dose for self-treatment.

Timing · Once daily at night, because the effect starts 8 to 12 hours after the dose.With food? · No source we read gave guidance on food. The EU monograph says senna should only be used if a change of diet or a bulk-forming agent has not worked.How long to trial · A single dose is a fair test, as the effect comes within about a day. If it has not worked or symptoms persist, the EU monograph advises seeing a doctor or pharmacist rather than increasing the dose or duration.

How people take it

Tablet or capsule (standardised extract)10–30 mg sennosides at nightStandardised products let you match the dose to the EU monograph. Check the label states sennosides.

Herbal tea (leaf)Follow the product labelThe EU monograph covers standardised comminuted leaf as a tea. Strength varies with steeping, so the dose is harder to control than with a tablet.

Liquid preparationFollow the product labelThe EU monograph allows standardised liquid forms. Some contain ethanol.

Safety

Who should avoid

Pregnancy and breastfeeding — EU monograph contraindicates it
Children under 12 — contraindicated by the EU regulator
Bowel obstruction, Crohn's disease, ulcerative colitis or appendicitis
Abdominal pain, nausea or vomiting of unknown cause — see a doctor first
Severe dehydration or electrolyte loss
Kidney disease — risk of electrolyte imbalance
Use every day or beyond 1 week — the cause should be investigated

Known interactions

AvoidLiquorice root — The EU regulator says not to use liquorice with stimulant laxatives, which can add to potassium loss; senna is a stimulant laxative.

CautionCorticosteroids (steroid tablets) — The EU monograph says adrenocorticosteroids may enhance potassium loss with senna, so patients taking them should consult a doctor first.

CautionDigoxin & heart-rhythm medication — Low potassium from laxative overuse strengthens cardiac glycosides and interacts with antiarrhythmics; the EU monograph also names QT-prolonging drugs and diuretics, so ask a doctor before combining.

CautionLiquorice root — Liquorice root, like diuretics and corticosteroids, may enhance potassium loss, which the EU monograph says means checking with a doctor before taking senna.

Compare with

Head-to-head pages for the pairs people search most.

Senna vs Psyllium

Questions people ask

How long can I take senna?

The EU regulator says not more than 1 week, and usually two to three doses in that week is enough. Longer use may impair bowel function and cause dependence, and if you need a laxative every day the cause of the constipation should be investigated.

How long does senna take to work?

Usually 8 to 12 hours, because bacteria in the large intestine have to convert it to its active form. That is why the EU monograph advises taking it once at night.

Is senna safe in pregnancy or for children?

No. The EU monograph contraindicates it in pregnancy, while breastfeeding, and for children under 12, citing genotoxicity concerns for related compounds in laboratory studies and small amounts of an active metabolite in breast milk. The Cochrane review of childhood constipation found almost no useful data on senna.

What side effects does senna cause?

Abdominal pain, cramps and loose stools are the main ones, especially at higher doses, and reducing the dose usually helps. Urine may turn yellow or red-brown, which is not clinically significant, and long-term use can cause water and electrolyte imbalance and harmless dark bowel lining that usually clears once it is stopped.

Sources

Last reviewed 29 September 2026 · Next review March 2027 · How we rate evidence