Pharmacodynamics is a major branch of pharmacology and is the study of drugs' physiological effects. Once a drug is introduced into a living system, the body undergoes a series of biochemical reactions. The effects on the body depend on how the drug is delivered or exposed to the bloodstream.
Pharmacodynamics mainly focuses on dose-response relationships, defined as the relationship between the concentration of drugs and their effect on the body. The pharmacodynamic model, known as the PD model, describes this dose-response relationship and the drug-receptor interaction. Drugs introduced into the body either induce or inhibit normal physiological processes.