Pharmacoepidemiology is described because they have a look at in actual situations and on large populations, of use, effectiveness and danger of drugs. The science of pharmacoepidemiology can answer a range of questions regarding how, why, when, where, and by whom a medicine is being used. It is a way of finding out the impact of a medicine as well as the usage results in a large, well-defined population. Also, it can help provide some indication as to how a particular drug is benefitting society and how it may be having a negative impact. Pharmacoepidemiology can be carried out both before and after a medicine is taken to market. They allow symbolizing conditions of use, misuse, medical effectiveness, detrimental drug reactions and risks of drugs.