Pharmacoepidemiology is that 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 event of pharmacoepidemiology should improve the "rational drug use". Pharmacoepidemiology is an emerging field to understand the use of medicines during an outsized population, identify and quantify adverse drug reactions during a population, and to quantify the danger or advantage of taking a drugs for a selected 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 within the connection to outcomes. Pharmacoepidemiology results are often utilized in conjunction with other data to elucidate or identify areas of need and improve the health outcomes.