Adverse drug events (ADEs) are injuries resulting from medical intervention related to a drug, causing morbidity and mortality in the population and generating substantial health care costs. Prescribing errors contribute to a large preventable portion of ADE. The aim of this study was to estimate the pharmacy cost of preventing ADE through pharmacist interventions on prescribing errors. Data was collected in 42 Norwegian pharmacies over 4 consecutive weeks in April 2016. The data was analyzed in terms of prescribing errors, interventions performed and time to resolve the issues. Cost was estimated based on average pharmacist salary and national insurance contributions for 2016. Sensitivity analysis was done on the cost estimate using minimum and maximum pharmacist salary for 2016. The sample comprised 39,750 dispensing processes of 71,833 items. 2822 prescribing errors were captured in 2545 dispensing processes of 6080 items, giving a rate of prescribing errors of 7.1%. The most frequent errors were adverse drug reactions (n=563, 20%), drug-drug interactions (n=560, 19.8%), dose errors (n=289, 10.2%). Other errors included amount/duration, drug choice, formulation and strength. 5279 interventions were done to resolve the issues, giving 1.9 interventions per prescribing error. The most frequent interventions were dialogue with patient (n=2073, 73.5%), pharmacist’s judgement (n=1222, 43.3%), reviewing patient profile (n=625, 22.1%) and contacting prescriber (n=482, 17%). Time spent on resolving prescribing errors was 12,684 minutes, of which 3,318 minutes were spent calling the prescriber. The resulting pharmacy cost estimate was USD 0.14 per prescription. With a total of 53,223,641 prescriptions dispensed annually, this equals USD 7,432,000 in 2016 (sensitivity analysis USD 0.12-0.17 per prescription, USD 6,395,000-9,150,000 per year). The costs to pharmacies for interventions directed to handle prescribing errors were USD 0.14 per prescription considering only the personnel costs.