It is extremely important that your colon be thoroughly cleaned before your colonoscopy. This will let the doctor see any abnormalities, such as colon polyps, during the procedure. Polyps are small growths in the colon that could later turn into cancer. Cleansing the colon before a colonoscopy is called bowel preparation, or prep. It involves taking medication that causes frequent, loose bowel movements to empty the colon. The medication is taken by mouth, and typically comes in liquid form. You will also need to change what you eat during the day or two before the colonoscopy.