What is Pharmacodynamics?

• A. The rate at which drugs are absorbed
• B. The mechanism of action of drugs
• C. What the drug does to the body
• D. What the body does to the drug

Answer: (C)

Pharmacodynamics is the study of how drugs produce effects in the body. It explains what the drug does to physiological systems—how it binds to targets like receptors or enzymes, the cellular changes that follow, and the resulting therapeutic or adverse effects. This includes how strong the effect is at a given dose (potency), how the effect grows with increasing dose (dose–response relationships), and how different drugs with similar targets can vary in efficacy. The concept contrasts with pharmacokinetics, which asks what the body does to the drug (absorption, distribution, metabolism, and excretion). For example, a drug may activate a receptor to produce analgesia, and blocking that receptor would reduce the effect. The mechanism of action is a facet of pharmacodynamics—the specific way a drug produces its effect—while the broader description is simply what the drug does to the body.