The three main types of laxatives commonly used by patients for colonoscopy are: mannitol, polyethylene glycol and sodium phosphate. The common adverse effects of these three types of laxatives are digestive symptoms, such as nausea, vomiting, bloating, abdominal pain or abdominal discomfort when drinking too fast or too hard. For mannitol, because mannitol produces some gas in the intestine after drinking, the use of mannitol for intestinal preparation, when doing colonoscopy should not be electrodesection or electrocoagulation, otherwise it will lead to adverse reactions such as colon explosion. When drinking sodium phosphate salt must pay attention to whether the patient has renal insufficiency, because it may lead to kidney failure, so the use of sodium phosphate salt must be cautious. The laxatives of this type of Hengkang polyethylene glycol are generally safe, except for digestive symptoms, a very small number of patients may have laxatives after drinking without defecation, then this is very rare. All in all, the most commonly used laxative in hospitals today is polyethylene glycol, which has fewer side effects on the human body.