Cleansing the bowel is essential for a successful colonoscopy. A doctor will provide specific instructions on how to do this. They may recommend: Dietary changes: The day before the procedure, it may be necessary to make some dietary changes, such as eating only a light breakfast and lunch with no evening meal or consuming a liquid-only diet. Laxatives: It is usually necessary to take laxatives the day before the procedure, either in pill or liquid form. Sometimes, a person may also need to take them on the morning of the colonoscopy.