Post-approval studies are studies that are conducted after a drug is approved. Such studies may be conducted for a variety of reasons, including to provide additional information on efficacy, safety, and use. For example, in some cases, a drug may be approved based on a surrogate endpoint that may predict clinical outcome. 

After approval, studies will be conducted to demonstrate the effect on clinical endpoints. 

Studies can be conducted in special populations, such as children and the elderly, to understand the effects of drugs in these populations. 

Safety studies may be conducted after marketing authorization to improve understanding of potential risks. Long-term follow-up studies or comparative studies between approved medicines can provide the medical community with important information about safety and efficacy. 

Post-approval studies included a range of designs and data sources.