Which of the following substances is not a CNS Depressant?

Cocaine is categorized as a central nervous system (CNS) stimulant rather than a depressant. Stimulants increase activity in the brain, leading to heightened alertness, increased energy, and enhanced mood. This is in stark contrast to CNS depressants, which work by slowing down brain function and can lead to sedation, relaxation, and decreased inhibition.

On the other hand, alcohol, barbiturates, and benzodiazepines all function as CNS depressants. They chemically induce relaxation by enhancing the effect of the neurotransmitter GABA (gamma-aminobutyric acid), which inhibits neural activity. This is exactly why they are utilized in medical settings for treatment of anxiety, insomnia, and seizures, among other conditions. By understanding these classifications, it's clear why cocaine stands apart as a CNS stimulant.