Which substance is classified as a central nervous system depressant?

A central nervous system depressant is a substance that slows down brain activity and can lead to a calming effect on the individual. Alcohol fits this definition distinctly because it acts directly on the central nervous system, causing relaxation, reducing anxiety, and impairing cognitive and motor functions.

In contrast, caffeine is a stimulant that increases alertness and energy; nicotine also acts as a stimulant, although it can have varying effects on relaxation and arousal depending on the context and dosage. Cocaine is another stimulant, which boosts energy levels and can lead to increased alertness and euphoria. Since alcohol slows down brain activity rather than stimulating it, it is the substance that is accurately categorized as a central nervous system depressant.