What is pharmacodynamics?

• A. The study of how drugs affect the body.
• B. The timing of drug administration.
• C. The study of how the body absorbs, distributes, metabolizes, and excretes drugs.
• D. The process of drug regulation.

Answer: (A)

Pharmacodynamics is about what the drug does to the body: how it produces its effects, through mechanisms of action and interactions with receptors, and how those effects change with different drug concentrations. It covers the dose–response relationship, potency, and efficacy—in other words, how the magnitude of the effect relates to the amount of drug at the site of action. For example, a pain reliever works by binding to receptors to block pain signals, and increasing the dose typically increases the analgesic effect up to a maximum. This contrasts with pharmacokinetics, which describes how the body handles the drug (absorption, distribution, metabolism, excretion) and mainly influences timing and amount reaching the site of action. Drug regulation is separate from pharmacodynamics.