Implementing successful interventions to support effective medication reconciliation is an ongoing challenge. The MARQUIS2 study examined whether system- and patient-level interventions plus physician mentors can improve medication reconciliation and reduce medication discrepancies. This analysis based on patient exposure in the MARQUIS2 study found that patient receipt of a best possible medication history (BPMH) in the emergency department and medication reconciliation at admission and discharge were associated with the largest reductions in medication discrepancy rates.