Which statement correctly describes pharmacodynamics?

• A. Time course of drug concentration in the body
• B. What the body does to the drug
• C. What the drug does to the body
• D. How the drug is excreted

Answer: (C)

Pharmacodynamics is about what the drug does to the body, including how it produces its effects through receptor interactions, the mechanism of action, and the relationship between dose and response. It explains why a drug produces analgesia, lowers blood pressure, or causes side effects, and how factors like receptor affinity, intrinsic activity, tolerance, and signaling pathways influence the magnitude and duration of those effects.

This is distinct from pharmacokinetics, which asks what the body does to the drug—absorption, distribution, metabolism, and excretion—and governs how drug concentrations change over time. So the statement that best describes pharmacodynamics is that it concerns what the drug does to the body.