Senna is a large genus of flowering plants belonging to the legume family, mostly (but not entirely) found in tropical regions. There are believed to be between 260 to 350 different species, with about 50 in cultivation. Senna extract is available as a powder, in pills and capsules, or as an ingredient in tea.
It is widely used as a non-prescription laxative to treat constipation, and can also clear the bowel for the performance of diagnostic tests like colonoscopy, or prior to surgery. Senna is also taken for irritable bowel syndrome (IBS), to ease haemorrhoids, and to encourage weight loss. It contains many active compounds called sennosides, which irritate the bowel lining and so promote peristalsis and evacuation.
Senna is barely absorbed by the body and may inhibit the reabsorption of water and electrolytes in the colon, enhancing the accumulation of intestinal fluid and increasing the moisture content of waste material.
The fruit of the plant seems not to have as strong an action as the leaf, leading to some warnings against senna leaf having ill effects if used long term, such as cramping, diarrhoea, unwanted weight loss and possible liver injury.