It is important to consider unintended consequences when implementing new tools, such as health information technology (HIT). This study reviewed 2,700 patient safety event reports to identify the type of medication error, the stage in the process in which the error occurred, and how HIT usability issues contributed to the errors. Errors in dosing were the most frequent type, and occurred during ordering or reviewing. Most errors described usability issues which should be considered and addressed to improve medication safety.