The main active ingredients in cascara sagrada are quinine compounds: most notably two separate types of anthraquinones and four closely related types of cascarosides. These compounds work by irritating the colon and thus triggering stronger and quicker movements in the intestine. A strong bowel movement will theoretically follow soon after. In addition, aloe-emodin seems to relax smooth muscles slightly, making the bowels more sensitive.
It may help in preventing the formation of gallstones, although this has not been fully studied.