Mannitol is a type of sugar alcohol which is also used as a medication. As a sugar, it is often used as a sweetener in diabetic food, as it is poorly absorbed from the intestines. As a medication, it is used to decrease high pressures in the eyes, seen in glaucoma, and to lower increased intracranial pressure. Medically, it is given by injection. Effects typically begin within 15 minutes and last up to 8 hours. Common side effects from medical use include electrolyte problems and dehydration.