Pharmacodynamics is the study of how drugs exert their effects on the body, including the mechanisms of action at molecular, cellular, and organ levels. It explains the relationship between drug concentration and the resulting biological response. This knowledge is crucial for understanding therapeutic effects and potential side effects. It focuses on drug-receptor interactions, signal transduction, and physiological outcomes, differentiating it from pharmacokinetics, which involves absorption, distribution, metabolism, and excretion. Understanding pharmacodynamics helps clinicians optimize drug dosing for maximum efficacy and safety.

Reference: Katzung BG, Basic and Clinical Pharmacology, 15th Edition.