Background Adverse drug events (ADEs) are a major cause of morbidity in hospitalised and ambulatory patients. Computerised provider order entry (CPOE) combined with clinical decision support systems (CDSS) are being widely implemented with the goal of preventing ADEs, but the effectiveness of these systems remains unclear.

Methods We searched the specialised database Agency for Healthcare Research and Quality (AHRQ) Patient Safety Net to identify reviews of the effect of CPOE combined with CDSS on ADE rates in inpatient and outpatient settings. We included systematic and narrative reviews published since 2008 and controlled clinical trials published since 2012.

Results We included five systematic reviews, one narrative review and two controlled trials. The existing literature consists mostly of studies of homegrown systems conducted in the inpatient setting. CPOE+CDSS was consistently reported to reduce prescribing errors, but does not appear to prevent clinical ADEs in either the inpatient or outpatient setting. Implementation of CPOE+CDSS profoundly changes staff workflow, and often leads to unintended consequences and new safety issues (such as alert fatigue) which limit the system's safety effects.

Conclusions CPOE+CDSS does not appear to reliably prevent clinical ADEs. Despite more widespread implementation over the past decade, it remains a work in progress.