The importance of pharmacoepidemiology is highlighted by variety of outstanding drug withdrawals in recent years. Each of these withdrawals was preceded by severe or fatal adverse effects that had been unrecognized or underappreciated at the time of approval. Exploitation the tools of pharmacoepidemiology, it's potential to spot adverse effects that will be unnoted in irregular trials as a result of those adverse effects square measure uncommon, represent a rise in risk from Associate in Nursing already high baseline (e.g., a rise in risk of infarction or stroke in older patients), occur primarily in patient teams underrepresented in clinical trials (e.g., the old, children, pregnant women), need several months or years to develop, occur primarily with co-administration of specific alternative medication, and/or occur primarily in patients with a particular comorbidity or genotype.