Senna is primarily used as a laxative to treat constipation and stimulate bowel movement prior to undergoing diagnostic procedures, such as a colonoscopy, notes WebMD. The medicated form of senna, extracted from the herb's fruit and leaves, is approved by the United States Food and Drug Administration.
Senna contains sennosides that aggravate the lining of the bowel wall to induce evacuation of the bowels. Oral administration of senna is likely effective in alleviating constipation and possibly effective in loosening the bowels right before a colonoscopy.
Senna is also used to treat hemorrhoids and irritable bowel syndrome. Some people also use this product for losing weight. However, as of 2015, there is inadequate scientific data to evaluate the efficacy of senna for any of these conditions, states WebMD.