Which of the following drugs is classified as a depressant?

Alcohol is classified as a depressant because it works primarily by slowing down brain function and neural activity. This action affects the central nervous system, leading to a range of effects including relaxation, drowsiness, and decreased inhibitions. Depressants typically reduce anxiety and create a calming effect, which is consistent with how alcohol influences behavior and cognition.

In contrast, the other substances listed have stimulant properties. Caffeine, for example, is well known for its ability to increase alertness and energy levels. Amphetamine also stimulates the central nervous system, leading to increased energy, focus, and euphoria. Cocaine is another stimulant, and it can produce intense feelings of euphoria and increased energy levels as well, primarily by enhancing the activity of dopamine in the brain. Thus, alcohol stands out among these substances as the one that depresses, rather than stimulates, CNS activity.