Final answer:
Depressants are drugs that lower neurotransmission levels in the brain and reduce arousal or stimulation. They are also known as "downers" as they lower the level of arousal when taken. The opposite drug class of depressants is stimulants, not antidepressants.
Step-by-step explanation:
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 occasionally referred to as "downers" as they lower the level of arousal when taken. Stimulants or "uppers" increase mental and/or physical function, hence the opposite drug class of depressants is stimulants, not antidepressants.