Mannitol injection is not a substitute for a laxative when doing a colonoscopy. Drinking mannitol before doing colonoscopy under the guidance of the doctor can play a role in inducing diarrhea and emptying the intestines. But mannitol is not a laxative, laxatives are a kind of lubrication of the intestine, promote defecation of drugs, mainly lactulose, sorbitol and so on. The two drugs are not interchangeable. Mannitol can reduce intracranial pressure, osmotic diuresis. In clinical practice, it is mainly used in the rapid intravenous infusion of cerebral edema and tissue dehydration. It should be noted that mannitol is used with caution in people with poor kidney function. When using mannitol, pay attention to observe the vascular condition to avoid phlebitis. It is recommended that Mannitol be used rationally under the guidance of a doctor.