[Pharmacoepidemiology: lights and shadows]

Adverse drug reactions are a major cause of illness and death. They cause 5-10% of general practice consultations and 5 to 10% of hospital admissions and would be the third or fourth cause of death (after heart attack, stroke and cancer). It is a failure of contemporary medicine. The purpose of pharmacoepidemiology is the study of drug use in populations and its impact on public health. The author describes the four stages of the recent history of pharmacovigilance. The first, spontaneous reporting, has identified many adverse drug reactions but cannot provide with incidence or risk estimates. Observational epidemiological research has shaped second generation pharmacovigilance, providing incidence and relative and absolute risks which are essential for public health decision taking. The meta-analysis of clinical trials would be third-generation pharmacovigilance: it has contributed to the understanding of relatively common adverse drug reactions with great impact on public health. Research on big data will surely be the basis of the fourth generation of pharmacovigilance.