Tolvaptan is a vasopressin receptor antagonist. Vasopressin (a.k.a. ADH or antidiuretic hormone) helps to regulate water retention by absorbing water in the collecting ducts of the nephron.

Vasopressin, also known as antidiuretic hormone (ADH), has two main functions: reducing the amount of urine released by the kidneys and helping raise blood pressure. Vasopressin is produced by the ...