GHB (gamma-hydroxybutyrate) is a central nervous system depressant, which means it slows down the messages travelling between the brain and the body. Although it is sometimes called liquid ecstasy, it is not chemically related to ecstasy and has an entirely separate chemical profile and effects.

GHB usually comes as a liquid, and is sold in vials, bottles or fish-shaped soy sauce containers. It is colourless but may have colour added (often blue) to stop it being mistaken for water or other clear liquids. It is odourless and can have either a bitter or a salty taste. Less often, GHB is found in the form of a white powder. GHB is usually swallowed but may be injected, snorted or inserted anally.