Medications represent the most common intervention in health care, despite their benefits; they also lead to an estimated 1.5 million adverse drug events and tens of thousands of hospital admissions each year. Although some are not preventable given what is known today, many types are, and one key cause which is preventable is drug-drug interactions (DDIs). Most electronic health record systems include programs that can check and prevent these types of interactions as a routine part of medication ordering. Studies suggest that these systems as implemented often do not effectively screen for these DDIs. A major reason for this deficiency is the lack of any national standard for the critical DDIs that should be routinely operationlized in these complex systems. We review the leading critical DDI lists from multiple sources including several leading health systems, a leading commercial content provider, the Leapfrog CPOE Testing Standard, and the new Office of the National Coordinator (ONC) DDI List. Implementation of strong DDI checking is one of the important steps in terms of realizing the benefits of electronic prescribing with respect to safety. Hopefully, the ONC list will make it easier for organizations to ensure they are including the most important interactions, and the Leapfrog List may help these organizations develop an operational DDI list that can be practically implemented. In addition, this review has identified 7 common DDIs that can be the starting point for all organizations in this area of medication safety.