Pharmacoepidemiology is the study of interactions between drugs and human populations, investigating, in real conditions of life, benefits, risks and use of drugs. Pharmacoepidemiology applies to drugs and their pharmacological evaluations, the different methods also used in epidemiology to assess in real conditions of life, benefits, risks and use of drugs. Pharmacoepidemiologic studies are ad-hoc studies or studies on databases. Specific methods exist to measure drug exposure, as well as indicators of compliance and misuse of drugs. Various designs for descriptive and explanatory studies exist, in a context in which a growing proportion of studies are carried out using medico-administrative data. The limits traditionally affecting the study designs are modified in this context, almost any design selected for the conduct of a study from these databases then deriving from a cohort in whom the information has been recorded prospectively and exhaustively.