Antidiuretic hormone (ADH), also known as vasopressin, is a peptide hormone produced by the hypothalamus and released by the posterior pituitary gland. It regulates water balance in the body by promoting water reabsorption in the kidneys, thus concentrating urine and reducing urine output. Clinically, abnormalities in ADH levels can lead to conditions such as diabetes insipidus or the syndrome of inappropriate antidiuretic hormone secretion (SIADH), impacting fluid balance and electrolyte homeostasis.