Pharmacoepidemiology has been distinct as the study of the allotment and determinants of drug associated events in populations and the point of this study to efficacious drug treatment. The word ‘drug’ in the implication is generally understood to have biologics, such as vaccines, and the populations are understood to be human. The emphasis is on studies of the safety and effectiveness of drugs used for medical purposes. Both randomized and nonrandomized (observational) designs are used, with the latter being more ordinary, especially for the study of adverse effects. Pharmacoepidemiology may be regarded as a sub order of both clinical epidemiology and clinical pharmacology.