Which of the following is an example of a depressant?

Alcohol is classified as a depressant because it directly impacts the central nervous system by slowing down brain activity and impairing cognitive functions. This results in decreased inhibition, slowed reactions, and a sense of relaxation, making it distinctly different from stimulants, which increase alertness and energy.

In contrast, the other substances listed are stimulants. Caffeine enhances alertness and reduces fatigue, cocaine increases dopamine levels leading to heightened energy and euphoria, and nicotine stimulates the release of neurotransmitters that can elevate mood and energy. Understanding these classifications helps in recognizing the effects different substances have on the body and mind.