Pharmacology is the branch of biology that studies drug action, exploring how chemical substances interact with living systems to produce a therapeutic or toxic effect. It is fundamentally concerned with two key areas: pharmacodynamics, which examines what a drug does to the body, including its mechanism of action; and pharmacokinetics, which describes what the body does to the drug, encompassing its absorption, distribution, metabolism, and excretion. By providing a deep understanding of these processes, pharmacology forms the scientific basis for the discovery, development, and safe clinical use of medicines to treat, cure, and prevent disease.