Medicine is two things at once. It is the science and practice of diagnosing, treating, and preventing disease. It is also the substances used to do that, though in that sense the word overlaps with medication and drug. The distinction is mostly context. A physician practices medicine. A patient takes medicine. The same word covers both.

The field has changed enormously in the past century. Antibiotics turned infections from killers into inconveniences. Vaccines eliminated smallpox and pushed polio to the brink. Chemotherapy, immunotherapy, and targeted therapies have extended survival for many cancers. Chronic diseases like diabetes and hypertension are now managed with drugs that let patients live near-normal lives. Surgery, imaging, and molecular diagnostics have transformed what doctors can see and do. At the same time, access to care remains uneven, and drug prices are a persistent source of tension.

Branches of medicine include:

• Internal medicine. Adult care, often in hospitals or clinics.
• Pediatrics. Care of infants, children, and adolescents.
• Surgery. Operative treatment of disease and injury.
• Psychiatry. Mental health and behavioral disorders.
• Public health. Population-level disease prevention and health promotion.

Evidence-based medicine, which integrates the best available research with clinical expertise and patient values, is the dominant framework in modern practice.