Gamma-hydroxybutyrate (GHB) is a short-chain fatty acid that naturally occurs in the brain, where it acts as a neurotransmitter and as a neuromodulator. GHB is a gamma-aminobutyric acid (GABA) analogue that passes the blood–brain barrier. GHB exerts its actions by binding to the GHB receptor in the brain, and in supraphysiologic concentrations, by binding to the GABAB receptor. Pharmaceutical GHB has a limited clinical use, e.g., in narcolepsy, but is nowadays well known as a party drug. Due to the narrow window of safety, GHB intoxications frequently occur, characterized by sudden coma, hypoventilation, and bradycardia. After weeks of repeated exposure, tolerance and dependence may occur. GHB-dependent patients use GHB "around the clock", to prevent withdrawal symptoms. Abrupt cessation of intensive GHB use may result in a severe GHB withdrawal syndrome, with delirium and agitation.