We develop a typology of clinicians' workarounds when using barcoded medication administration (BCMA) systems. We then identify the causes and possible consequences of each workaround. BCMAs usually consist of handheld devices for scanning machine-readable barcodes on patients and medications. They also interface with electronic medication administration records. Ideally, BCMAs help confirm the "five-rights of medication administration:" right patient, drug, dose, route, and time. BCMAs are reported to reduce medication administration errors-the least likely medication error to be intercepted--although these claims have not been clearly demonstrated. We studied BCMA use at five hospitals by: 1-observing and shadowing nurses using BCMAs at two hospitals; 2-interviewing staff and hospital leaders at five hospitals; 3-participating in BCMA staff meetings; 4-participating in one hospital's failure-mode-and-effects analyses; 5-analyzing BCMA override log data. We identified 15 types of workarounds, including, for example, affixing patient-ID-barcodes to computer carts, scanners, doorjambs, or nurses' belt-rings; carrying several patients' pre-scanned medications on carts. We identified 31 types of causes of workarounds, such as, unreadable medication-barcodes (crinkled, smudged, torn, missing, covered by another label); malfunctioning scanners; unreadable or missing patient-ID-wristbands (chewed, soaked, missing); non-barcoded-medications; failing batteries; uncertain wireless connectivity; emergencies. We found nurses overrode BCMA-alerts for 4.2% of patients charted and for 10.3% of medications charted. Consequences of the workarounds include administration of wrong medications, doses, times, and formulations. Shortcomings in BCMAs' design, implementation and workflow integration encourage workarounds. Integrating BCMAs within real-world clinical workflows requires attention to use in situ to ensure safety features correct use.