Which statement defines pharmacodynamics?

• A. What the drug does to the body
• B. What the body does to the drug
• C. The rate of drug excretion
• D. The distribution of the drug in tissues

Answer: (A)

Pharmacodynamics describes the effects a drug has on the body, including how it produces its therapeutic or adverse responses at the cellular or systemic level—through mechanisms like receptor binding, signaling pathways, and dose–response relationships. This area covers how the magnitude of the effect changes with concentration, and concepts such as efficacy and potency. It’s the opposite of pharmacokinetics, which is about what the body does to the drug—absorption, distribution, metabolism, and excretion. So the statement that best defines pharmacodynamics is the one describing what the drug does to the body; the other options refer to how the body handles the drug or what happens to the drug as it moves through and is eliminated from the body.