Which of the following is the most widely used and abused CNS depressant?

The most widely used and abused CNS (central nervous system) depressant is alcohol. Alcohol acts as a depressant by inhibiting the function of the CNS, leading to effects such as decreased anxiety, impaired motor function, and reduced inhibitions. This can also result in drowsiness and sedation, especially at higher doses. Given its legal status and widespread availability, alcohol consumption is prevalent across many demographics.

In contrast, while heroin is indeed a potent CNS depressant, it is less commonly used compared to alcohol, primarily due to its status as an illegal substance with significant stigma and risk associated with its use. Caffeine is a stimulant, which actively increases alertness and energy rather than causing sedation or depressant effects. Marijuana, often debated in legal and social contexts, is generally classified as a hallucinogen or can have both stimulant and depressant effects depending on the strain and dosage, but it does not rival alcohol in terms of widespread use and abuse as a depressant. Therefore, alcohol is the clear choice as the most prevalent CNS depressant in terms of both use and abuse.