Which of the following is a common stimulant?

Cocaine is classified as a common stimulant due to its effects on the central nervous system. Stimulants are substances that increase the activity of the brain and nervous system, leading to heightened alertness, increased energy, and improved mood. Cocaine achieves this by increasing the levels of dopamine, a neurotransmitter associated with pleasure and reward, in the brain. This results in temporary feelings of euphoria and increased energy, which are characteristic effects of stimulants.

In comparison, other substances listed have different classifications. Heroin is an opioid and acts as a depressant, leading to sedation and pain relief rather than stimulation. Alcohol, while often socially categorized as a recreational substance, is also a depressant that can slow down brain function and impair coordination. Tranquilizers are medications designed to calm or sedate, which serves to further contrast them from stimulants. Overall, the unique properties of cocaine firmly establish it within the stimulant category.