Senna is a natural medicine containing sennosides that are derived from the leaves of the senna plant. Sennosides irritate the lining of the bowel causing a laxative effect. Senna has been used in alternative medicine as a laxative and an aid to treat constipation. Not all uses for senna have been approved by the FDA. It should not be used in place of medication prescribed for you by your doctor. Senna should not be used in place of medication prescribed for you by your doctor.