Mannitol belongs to the high osmolality class of drugs and can also treat constipation. When patients take mannitol, it will increase the intestinal osmotic pressure, resulting in the intestinal wall of water is absorbed into the intestine, thus increasing the water content of feces, promoting the rapid discharge of intestinal contents, and relieving constipation. However, mannitol should not be taken for a long time, after long-term use will lead to intestinal osmotic pressure disorders, the intestinal wall due to a large amount of water shortage, and aggravate constipation. In addition, a large number of long-term application of mannitol, easy to induce patients with electrolyte disorders, so that patients with dehydration, urine, shock, etc., so when the patient’s treatment of constipation, should not be preferred mannitol. It is recommended to use medication under the guidance of a doctor, not blindly self-medication, in order to avoid adverse effects.