A depressant, or central depressant, is a drug or endogenous compound that lowers or depresses arousal levels and reduces excitability. Depressants are also occasionally referred to as "downers" as they lower the level of arousal when taken. Stimulants or "uppers" increase mental and/or physical function are the functional opposites of depressants.
Depressants are widely used throughout the world as prescription medicines and as illicit substances. When these are used, effects often include anxiolysis, pain relief, sedation or somnolence, and cognitive/memory impairment, as well as in some instances euphoria, dissociation, muscle relaxation, lowered blood pressure or heart rate, respiratory depression, and anticonvulsant effects, and even complete anesthesia or death at high doses.
Depressants exert their effects through a number of different pharmacological mechanisms, the most prominent of which include facilitation of GABA or opioid activity, and inhibition of glutamatergic or catecholaminergic activity.