For afternoon gastroenteroscopies, laxatives are usually started eight hours before the exam and finished within the first six hours. The specific time of the exam varies, so the time to drink the laxative varies. Gastroscopy is an examination of the esophagus, stomach, duodenum and other parts of the body with a gastroscope passing through the mouth; enteroscopy is an examination of the colon, rectum and other parts of the body with an enteroscope passing through the anus. Gastroenteroscopy can observe whether the mucosa of the gastrointestinal tract has inflammation, erosion, ulcers, polyps, tumors and other diseases. It is usually necessary to fast for six to eight hours before a gastroenteroscopy, so you should not eat or drink in the morning or at noon when you have a gastroenteroscopy in the afternoon. Eat a light diet the day before the exam and do not drink alcohol. About eight hours before the examination, you need to take mannitol, compound polyethylene glycol electrolyte dispersions and other drugs, which need to be taken within six hours before the examination. Be sure to take bowel cleansing medication under the guidance of your doctor, and it is not recommended to take the medication on your own, so as not to affect the effect of the examination.