Which of the following is a common street drug categorized as a stimulant?

Cocaine is commonly recognized as a stimulant, primarily due to its effects on the central nervous system. It increases alertness, feelings of euphoria, energy, and talkativeness by acting on the brain's dopamine system. Its powerful stimulant properties can lead to physical and psychological dependence, making it a significant concern in the context of addiction.

In contrast, heroin is classified as an opioid and works primarily as a depressant, affecting the body by slowing down the central nervous system. LSD is a hallucinogen, which alters perceptions and can cause visual and auditory hallucinations rather than stimulating the body. Ecstasy, while often seen as a stimulant because it can increase energy and sociality, also has hallucinogenic properties and thus doesn't fit neatly into the stimulant category. Therefore, cocaine stands out as the clear stimulant among the options provided.