Introduction Although medication errors may cause significant morbidity and mortality, the true cost of avoidable harm from such errors is unclear. While studies describe different methods for calculating a financial cost from an error, there remains variability in the way calculations are conducted depending on the clinical context. This review aimed to investigate the range of approaches for calculating medication error costs across healthcare settings.

Methods A systematic review was carried out with a duplicate data extraction approach and mixed methods data synthesis. Medline, Embase and Web of Science were searched for studies published between 1993 and 2015. Studies that explicitly described a method for calculating medication error cost were included. The variables used for the calculations and a description of the approach for calculating errors were reported.

Results 21 studies were included in the final review. There was wide variation in the way calculations were undertaken, with some calculations using a single variable only and others using several variables in a multistep approach. Few calculations included indirect costs, such as loss of earnings for the patient, and only one calculation considered opportunity cost. The majority of studies presented direct medication error costs whereas others approximated error costs from the savings made following an intervention.

Conclusions There are a wide range of methods used for calculating the cost of medication errors. The diversity arises from the number of variables used in calculations, the perspective from which the calculation is conducted from, and the degree of economic rigour applied by researchers.