A high proportion of hospitalizations is attributable to the prevalence of
adverse drug events. This retrospective study included outpatients and inpatients to determine the prevalence of
adverse drug events and if
polypharmacy increases it. The prevalence, classification, and causality of
adverse drug events were assessed based on medical records, laboratory values, and other data. Multivariate analysis (multiple logistic regression analysis) was performed with the presence or absence of
adverse drug events at the time of the visit as the dependent variable and items for which the P-value was <0.25 in the univariate analysis as independent variables. The prevalence of
adverse drug events was 13.0%, 10.9%, and 16.0% among all patients, the outpatient group, and the inpatient group, respectively. Multivariate analysis showed that
polypharmacy (≥5 drugs) significantly increased the risk of
adverse drug events in all patients. The prevalence of
adverse drug events significantly increased with each additional drug used. We expect that minimizing the number of medications through moderation of the number of
prescription drugs and elimination of
polypharmacy will reduce the number of outpatient visits and hospitalizations due to
adverse drug events.