This review assessed the effects of computerised physician order entry, automated dispensing machines, bar coding and computerised medication administration records on the likelihood of medication errors and adverse drug events. The authors' conclusion, that there was limited evidence in support of these technologies, is likely to be reliable. Authors' objectives To assess the effect of computerised physician order entry (CPOE), automated dispensing machines (ADMs), bar coding and computerised medication administration records (CMARs) on medication errors and adverse drug events (ADEs). Searching PubMed was searched from 1982 to March 2002 for studies published in peer-reviewed journals; the MeSH terms were stated. The reference lists in identified studies and previous reviews were also checked. Only studies that were published in full were included. Guidelines for implementation, reviews and user-satisfaction surveys were excluded. Study selection Study designs of evaluations included in the review Controlled studies were eligible for inclusion. The included studies were prospective controlled studies (including timeand-motion studies and crossover studies), prospective time series with historical control, prospective and retrospective before-and-after studies, and retrospective time series. Specific interventions included in the review Studies of CPOEs, ADMs, bar coding and CMARs were eligible for inclusion if they were conducted in the USA. Studies of clinical decision support systems were excluded. Most of the included studies of CPOE were conducted in institutions and, in all studies, CPOE systems were developed internally. Participants included in the review The inclusion criteria were not specified in terms of participants. Outcomes assessed in the review Studies that assessed medication errors and ADEs (the primary outcomes in the review) or other outcomes were eligible for inclusion. In the review, medication errors were defined as 'any preventable event that may cause or lead to inappropriate medication use or patient harm while the medication is in the control of the health care professional, patient or consumer'. ADEs were defined as 'any response to a drug which is noxious, unintended, and which occurs at doses normally used in humans for the prophylaxis, diagnosis or therapy of disease'. Some studies in the review reported results for different categories of ADEs (preventable and potential) and medication errors (errors in dosage, missed doses, non missed doses and wrong time). The review also assessed the appropriateness of the use of these interventions, where appropriateness was defined as the 'degree to which the technology was used as intended'. Other outcomes included the use of specific drugs, the time required to carry out various tasks, the number of drugs prescribed, hospital stay and the duration of therapy. How were decisions on the relevance of primary studies made? The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.