Stimulants are defined as?

• A. Drugs that slow down the central nervous system.
• B. Drugs that alter immune response.
• C. Drugs that reduce appetite only.
• D. Drugs that act on the central nervous system, speeding up messages to and from the brain.

Answer: (D)

Stimulants are drugs that act on the central nervous system to speed up the messages between the brain and the body. Because they boost CNS activity, they tend to make you more alert and energetic, and can raise heart rate and blood pressure. This matches the description of drugs that act on the brain and nervous system, speeding up the signals to and from the brain.

Think about why the other ideas don’t fit: slowing the central nervous system describes depressants, which calm rather than energize. Altering immune response isn’t the defining effect of stimulants. Reducing appetite can happen with some stimulants, but it isn’t what defines them.