Laxatives are usually required 4-6 hours in advance for a colonoscopy, but for constipated patients, laxatives are required 3 days or even a week in advance. The most widely used oral bowel cleansers in clinical practice are compounded polyethylene glycol electrolyte bulk, sodium phosphate salts, magnesium sulfate, and mannitol. It is recommended to avoid giving them all at once and to take them in divided doses for better results. They are given orally at a rate of approximately 1 to 1.5 liters per hour. In most cases, a bowel movement will begin after about 1L of the medicine has been given. If there is no bowel movement after about 1L of the medicine has been given, re-administer the medicine after confirming that there is no vomiting or abdominal pain, and observe closely until a bowel movement occurs. Bowel preparation is complete when the stool is yellow, transparent, non-dregs watery stool. Patients are advised to go to the regular hospital for colonoscopy and take oral laxatives as prescribed.