Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) is a condition where the body produces excessive amounts of antidiuretic hormone (ADH). This hormone helps regulate water balance in the body by controlling how much water the kidneys reabsorb. When too much ADH is released, it leads to water retention, dilution of blood sodium levels, and can cause symptoms like headache, nausea, and confusion. The causes of SIADH can vary and may include lung diseases, certain medications, or brain injuries. Diagnosis typically involves blood tests to check sodium levels and urine tests to measure ADH levels. Treatment focuses on addressing the underlying cause and managing fluid intake.