High-alert medications are drugs that bear a heightened risk of causing significant patient harm when they are used in error. Although mistakes may or may not be more common with these drugs, the consequences of an error with these medications are clearly more devastating to patients. Based on error reports submitted to the USP-ISMP Medication Errors Reporting Program and reports of harmful errors in the literature, ISMP created a list of potential high-alert medications. During August and September, 2003, more than 350 practitioners responded to an ISMP survey designed to identify which of these medications were most frequently considered highalert by individuals and organizations. Further, to assure relevance and completeness, the clinical staff at ISMP, members of our advisory board, and safety experts throughout the US were asked to review the potential list. The following list of 30 drugs and drug categories reflects the collective thinking of all who provided input. We hope you will use this list to determine the medications that require special safeguards to reduce the risk of errors. This may include strategies like limiting access to these medications, using auxiliary labels and automated alerts, standardizing the ordering, preparation, and administration of these products, and employing automated or independent double checks when necessary. (Note: manual double checks are not always the optimal error reduction strategy and may not be practical for a few of the medications on the list.)