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 the methods and/or reasoning of both pharmacology and epidemiology. The development of pharmacoepidemiology should improve the "rational drug use". Pharmacoepidemiology is an emerging field to understand the use of medications in a large population, identify and quantify adverse drug reactions in a population, and to quantify the risk or benefit of taking a medication for a particular disease or condition. Increasingly, secondary data are becoming more available with computerization of medical records and billing procedures. Pharmacoepidemiology has established and robust study designs that provide strong evidence for the drugs in the relationship to outcomes. Pharmacoepidemiology results can be used in conjunction with other data to explain or identify areas of need and improve the health outcomes.