Which of the following drugs is classified as a CNS depressant?

Ethyl alcohol is classified as a central nervous system (CNS) depressant because it slows down brain function and activity. When consumed, ethyl alcohol interacts with neurotransmitter systems, particularly enhancing the effects of gamma-aminobutyric acid (GABA), which leads to sedative effects. This results in a decrease in alertness, slowed reaction time, and impaired motor coordination.

In contrast, THC (the active ingredient in marijuana) and marijuana itself are primarily classified as cannabinoids and can have varying effects, including both depressant and stimulant properties, depending on the dosage and individual response. Cocaine, on the other hand, is a powerful CNS stimulant that increases the levels of dopamine in the brain, leading to heightened alertness and energy, which is the opposite effect of a CNS depressant. Therefore, ethyl alcohol is the clear example of a CNS depressant among the options provided.