Which substance is classified as a CNS depressant?

Alcohol is classified as a central nervous system (CNS) depressant because it decreases brain activity, leading to a range of effects including relaxation, sedation, and impaired cognitive and motor functions. This classification is based on how alcohol influences neurotransmitter activity, particularly by enhancing the effect of gamma-aminobutyric acid (GABA), which suppresses neuronal excitability.

In contrast, substances such as caffeine, nicotine, and MDMA function differently. Caffeine is a stimulant that increases alertness and can lead to heightened energy levels. Nicotine also acts as a stimulant in many contexts, promoting increased heart rate and alertness, although it may have varying effects depending on the dose and the user's tolerance. MDMA, often associated with recreational use, has stimulant properties as well and can elevate mood and energy levels, further distinguishing it from depressants like alcohol.