A natural or synthetic therapeutic agent having the property of inducing relaxation and varying degrees of depression of the central nervous system. The major types of sedatives are (1) chlorine substitution products (chloral hydrate, chlorobutanol); (2) ethanol derivatives (ethyl carbamate, hedonal); (3) specific aldehydes and ketones (paraldehyde, amylene hydrate), (4) barbituric acid derivatives (barbital, barbiturates). Sedatives are almost always prescription drugs.See Psychotropic Drug.