γ-Hydroxybutyric acid (GHB), also known as 4-hydroxybutanoic acid, is a naturally occurring neurotransmitter and a psychoactive drug. It is a precursor to GABA, glutamate, and glycine in certain brain areas. It acts on the GHB receptor and is a weak agonist at the GABAB receptor.

GHB has been used in a medical setting as a general anesthetic and as a treatment for cataplexy, narcolepsy, and alcoholism. It is also used illegally as an intoxicant, as an athletic performance enhancer, as a date rape drug, and as a recreational drug. It is commonly used in the form of a salt, such as sodium γ-hydroxybutyrate (Na.GHB, sodium oxybate, or Xyrem) or potassium γ-hydroxybutyrate (K.GHB, potassium oxybate).

GHB is also produced as a result of fermentation, and is found in small quantities in some beers and wines, beef and small citrus fruits.