A depressant, or central depressant, is a drug that lowers neurotransmission levels, which is to depress or reduce arousal or stimulation, in various areas of the brain. Depressants are also colloquially referred to as downers as they lower the level of arousal when taken.Stimulants or "uppers" increase mental or physical function, hence the opposite drug class of depressants is stimulants ... More @Wikipedia
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