What is the study of a drug's effects on the body?

• A. Pharmacokinetics
• B. Bioavailability
• C. Pharmacodynamics
• D. Metabolism

Answer: (C)

Understanding how a drug acts inside the body is pharmacodynamics. This field looks at the effects the drug has on physiology and biochemistry—how it interacts with receptors, the mechanism of action, and how the response changes with different doses (dose–response). It also covers therapeutic effects and potential adverse effects, helping explain why a medicine can relieve symptoms at one dose and cause side effects at another, and why responses vary between patients.

Pharmacokinetics, on the other hand, describes what the body does to the drug—how it is absorbed, distributed, metabolized, and eliminated. Metabolism is part of that processing, and bioavailability refers to the fraction that reaches systemic circulation. Since the question focuses on the body's effects produced by the drug, pharmacodynamics is the best fit.