A diuretic is any substance that promotes diuresis (increased urination and the physiologic process that produces such an increase involving extra urine production in the kidneys as part of the body’s homeostatic maintenance of fluid balance), the increased production of urine. This includes forced diuresis. There are several categories of diuretics. All diuretics increase the excretion of water from bodies, although each class does so in a distinct way. Alternatively, an antidiuretic, such as vasopressin (antidiuretic hormone), is an agent or drug which reduces the excretion of water in urine.