Pharmacoepidemiology studies the use and effects of drugs on large groups of people and patients. It assesses probability of beneficial and adverse effects, and risks for humans while using a particular drug.

Pharmacoepidemiology bridges pharmacology and epidemiology and borrows their methodology from both of them. It uses descriptive epidemiological method by describing exposure to a drug and by calculating rates, e.g., incidence and prevalence. Such descriptive method generates hypothesis about influence of the drug, but does not test it. Pharmacoepidemiology also uses analytic epidemiological method by means of observation (case-control and cohort studies) and experimentation (clinical trial). The analytic study compares an exposed group with a control group and serves as testing of the hypothesis.