Educational information, not medical advice — ask your doctor or midwife.
Senna is a herbal laxative made from the dried leaves and pods of Senna alexandrina. People take it for short-term relief of constipation. It does work, and human trials back that.
In France the herb was called séné, and it has a long place in European folk practice. But it is more than folklore now. Senna is a licensed over-the-counter medicine in the UK, the US and much of Europe.
Traditional standing is not proof that something works, and it is not proof that it is safe. Senna is unusual: the effect is proven, but the risks are real. Overuse can cause cramps, fluid loss and low potassium.
The laxative effect of senna is well established in people. The plant contains sennosides, which pass through the small bowel unchanged.
Bacteria in the colon turn sennosides into rhein anthrone, the active form. This acts on the lining of the large bowel. It speeds up the muscle waves and pulls water into the stool.
The result is a softer stool and a strong urge to go. Most people respond 6 to 12 hours after a dose. That delay is why labels suggest taking it at night.
The old folk idea that senna "cleans toxins out" is not supported. It moves the bowel. It does not detoxify the body.
Long use can stain the colon lining dark brown, a change called melanosis coli. It is harmless and fades after stopping. Whether long use weakens the bowel muscle is still argued, and the evidence is weak either way.
Senna is sold both as a licensed over-the-counter laxative and as a loose herb.
Tablets and capsules are the most common form. The label states the sennoside content, so the strength is known.
Syrups and liquid drops are used when tablets are hard to swallow. Many are made for children and are meant for use on medical advice.
Dried leaf and pod are sold loose for tea, sometimes blended with fennel or anise. Strength varies a lot from cup to cup, which makes the amount hard to judge.
Senna also hides inside other products. "Bowel cleanse" blends, slimming teas and some "flat tummy" teas contain it, often without making the laxative action clear.
Senna entered European medicine through Arabic physicians, who wrote about it from around the 9th century. Traders carried the dried leaf and pod west along Mediterranean routes.
By the late Middle Ages it was listed in European pharmacopoeias (official drug lists). French texts named it séné. Village healers and apothecaries used it as a purge for "sluggish" bowels.
It also appeared in spring "cleansing" routines, often mixed with liquorice or anise to soften the griping. In the 20th century senna moved from the folk shelf to the pharmacy shelf. It became one of the first herbs accepted as a standard over-the-counter drug.
Stop and see a doctor if any of these happen.
You get no bowel movement at all after using it, or you have rectal bleeding or black stools. You have severe cramps, ongoing vomiting, or a swollen, tender belly.
You feel weak, dizzy or shaky, or your heart feels like it is skipping or racing. These can signal fluid loss or low potassium.
Also book an appointment if constipation lasts more than two weeks, if it is new for you and you are over 50, or if it comes with weight loss you did not plan.
In the UK, the US and most of the EU, senna is a legal over-the-counter laxative medicine. It is also sold as a herbal tea and in food supplements. Rules on labelling and warnings vary by country.
Evidence grades and traditional-use labels are explained in our methodology. Nothing here is medical advice.
What it is typically used for, usual dose, cautions, and the study behind it where real trial data exists.
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