How Dulcolax Works Dulcolax contains the active ingredient Bisacodyl, a naturally occurring compound that helps to encourage a natural bowel movement. The Bisacodyl is combined with a waxy substance that is firm at room temperature but melts inside the body once it is inserted into the rectum. It is designed for short-term use. How To Use Dulcolax Children under 10: One suppository should be inserted into the rectum daily until symptoms subside. Dulcolax should not be used if the child has dehydration, anal fissues, inflammatory bowel disease or acute appendicitis. Do not exceed the recommended dosage.