Electronic health record implementation has improved safety through mechanisms such as computerized provider order entry (CPOE), but it has also had unintended adverse effects on patient safety. Reviewing incident reports from the US Pharmacopeia where CPOE was a contributing factor, this study sought to determine whether current CPOE systems are vulnerable to similar errors. Investigators then entered potentially problematic medication orders in various CPOE systems using a simulated approach. They encountered multiple usability hurdles including confusion with critical and irrelevant alerts, workflow issues, and variability in how orders were entered. These results demonstrate the need for robust independent usability testing of CPOE within electronic health records to support patient safety.