Have you ever taken over the counter or prescription drug? Are you curious about how these drugs are developed, approved and brought to the market? We begin by providing an overview of drug development and approval process and the role regulatory agencies, such as the US Food and Drug Administration, play in the approval process. We discuss phases of clinical trials – phases 1, 2, 3 and 4 – to evaluate efficacy and safety of drug products, along with case studies. We define pharmacoepidemiology – a scientific discipline to study use, safety and effectiveness of medical products and interventions – and the role it plays throughout the drug life cycle with relevant case studies. We also discuss how pharmacoepidemiology informs regulatory, policy and clinical decisions. Finally, we provide high-level overview of essential tools – study protocols, data sources, study designs and analysis – to conduct pharmacoepidemiologic studies.