A colonoscopy requires bowel preparation to clean out the large intestine so the doctor can clearly examine it for problems. This involves fasting from solid foods starting the day before the procedure, drinking only clear liquids to cleanse the colon, and stopping all liquids at midnight the night before. Patients may experience side effects like frequent bowel movements, nausea, bloating, and cramps during the cleansing process. They should stay hydrated, except for stopping liquids at midnight, and make arrangements for someone to drive them home after the procedure as they are not allowed to drive or use public transportation.