Antidiuretic hormone (ADH), also known as vasopressin, is a hormone produced by the hypothalamus and stored in the pituitary gland. Its primary function is to regulate the body's water balance by promoting water reabsorption in the kidneys, which helps to concentrate urine and reduce water loss. When the body is dehydrated or has high blood osmolarity, ADH is released into the bloodstream. This hormone signals the kidneys to retain water, leading to less urine production. Proper levels of ADH are essential for maintaining fluid balance and preventing conditions like diabetes insipidus, which can result from insufficient ADH.