A recent study conducted by the American Society of Health-System Pharmacists (ASHP) reviewed over 5,000 medication errors to discover why and how such errors occurred. According to the National Coordinating Council for Medication Error Reporting and Prevention (NCCMERP), a medication error is any preventable event that may cause or lead to inappropriate medication use or patient harm while the medication is in control of the health care professional, patient or consumer. Medication errors can be attributed to a number of factors including diagnosis errors and improper prescribing, dispensing, and administering of a drug.

The society examined 5,366 medical errors reported to the Food and Drug Administration's (FDA) Adverse Event Reporting System (AERS) from 1993 to 1998. Of these, 469 errors resulted in death. The age distribution ranged from new borns to men and women over 90. A surprising 380 deaths were linked to human factors such as improper drug administration, dose miscalculation, wrong drug preparations and limited drug knowledge. Ninety-two deaths resulted from communication mistakes, which included misinterpretation of orders, written miscommunication errors such as the improper labeling of drugs, and oral miscommunication errors. Several nurses incorrectly administered drugs because they misunderstood a physician's oral instructions. A small number of deaths resulted from manufacturer error. In addition, wrong directions were printed on several drug labels.

The ASHP concluded that systemic changes need to be made and product information improved in order to limit medication errors.