['The purpose of this study is to investigate the nature, frequency, and determinants of drug therapy alerts generated by a clinical decision support system (CDSS) in community pharmacy in order to propose CDSS improvement strategies.', 'This is a retrospective analysis of dispensed drugs and drug therapy alerts generated by a CDSS in community pharmacies.', 'Data were extracted from the CDSS of 123 community pharmacies. After taking a 10% random sample of patients with a prescription in the period August 2013-July 2014, 1,672,169 dispensed prescriptions from 81,742 patients were included in the analysis. Of all processed prescriptions, 43% led to one or more drug safety alerts, most frequently drug-drug interaction alerts (15% of all prescriptions), drug-disease interaction alerts (14%), duplicate medication alerts (13%), and dosing alerts (7%). The majority of prescriptions with alerts (80%) were clustered in a minority of patients (16%). The therapeutic drug group of the prescribed drug was the most important determinant of alert generation. Prescriptions for antithrombotic agents accounted for 9.4% of all prescriptions with an alert, beta-blocking agents for 7.5% and angiotensin-converting-enzyme inhibitors for 6.1%.'] Does nature and frequency of drug therapy alert generated by clinical decision support in community pharmacy?