Adverse drug events (ADE) are a leading cause of mortality in the United States. Recent studies have demonstrated a high level of complex medication regimens in institutionalized residents. Evidence of the relationship between medication regimen complexity (MRC) and ADE-related rehospitalizations or emergency department (ED) visits is evolving. Therefore, there is a demand for better characterization and study of MRC as an objective identifier to quickly screen and prioritize high-risk patients for follow-up medication management therapy. This manuscript will serve as a brief summary review of the current findings regarding the relationship between MRC and hospital readmission and ED usage and provide strategies for pharmacists to more efficiently evaluate complex medication regimens and optimize therapies.