Bowel movements normally start after 1-2 hours after drinking a laxative with a colonoscopy, but some patients start bowel movements after half an hour or 3-4 hours. Usually patients with normal bowel habits will start to have a bowel movement 1-2 hours after taking the laxative, but some patients start to have a bowel movement after half an hour or 3-4 hours. If there is constipation, or activity is relatively small, it may be 4 hours after taking laxatives to start defecation, through clockwise massage of the abdomen, moderate activity and other methods to increase intestinal peristalsis. In addition, no matter how long it takes to start a bowel movement, you should pass watery stools before having a colonoscopy. Patients should strictly follow the doctor’s instructions for the preparation of the intestines before the examination, maintain a good mood during the examination and avoid excessive tension.