Senna is an herb that contains sennosides, chemicals found in the leaves of the herb, which stimulate the colon muscles to contract by causing irritation to the bowel tissue. Sennosides also help retain water inside the intestines, causing them to move, says WebMD.
Senna, described as a stimulant laxative, is used to treat the pain and discomfort of constipation. It is also used to empty the bowel prior to surgery or invasive rectal examinations and tests such as colonoscopy, according to WebMD.
Senna is an FDA-approved supplement that is available without a prescription in the form of a liquid, chewable tablets, powder and dissolvable strips. Most adults and children over the age of 2 are able to take the medicine safely for short-term use of up to seven days. A bowel movement usually takes place between six to 12 hours after consuming the required dose, says WebMD.
Senna is also available in the form of a suppository that can be inserted directly into the rectum via the anus, bringing about a swifter bowel movement, says MedicineNet.
Senna is both a brand name and the generic name for the medicine, which is also sold under a variety of different brand names, according to Drugs.com.