Which phrase best describes a psychoactive drug?

• A. A chemical that affects brain activity and mood
• B. Medications that treat physical pain
• C. Substances with no impact on behavior
• D. Vitamins with no risk

Answer: (A)

Psychoactive drugs are chemicals that affect brain activity and mood by altering neurotransmitter signaling in the central nervous system, which in turn changes thoughts, feelings, and behavior. That defining effect—altering brain function to change mood and behavior—is why the description “a chemical that affects brain activity and mood” is the best fit. Other descriptions miss the core feature: treating physical pain describes a use, not the brain-based effect; claims of no impact on behavior falsely imply they don’t affect the brain; and vitamins with no risk don’t capture the brain-altering aspect. Examples include substances like alcohol, caffeine, and various prescription medications that change mood or perception by acting on brain chemistry.