Randomized controlled trials are considered the gold standard in the hierarchy of research designs for evaluating the efficacy and safety of a treatment intervention. However, their results can have limited applicability to patients in clinical settings. Observational studies using large health care databases can complement findings from randomized controlled trials by assessing treatment effectiveness in patients encountered in day-to-day clinical practice. Results from these designs can expand upon outcomes of randomized controlled trials because of the use of larger and more diverse patient populations with common comorbidities and longer follow-up periods. Furthermore, well-designed observational studies can identify clinically important differences among therapeutic options and provide data on long-term drug effectiveness and safety.