Medication Regimen Complexity and Patient-Reported Adverse Drug Events in Korean Community Pharmacies: A Cross-Sectional Study.

Evidence linking medication regimen complexity to patient-reported adverse drug events (ADEs) is limited. This study examined the association between regimen complexity and patient-reported ADEs among adults using community pharmacy services. A cross-sectional survey was conducted among adults with prescription experience at community pharmacies in Korea (14 January-24 February 2025). Data included MRCI-K scores, medication adherence, ADE reports, comorbidities, polypharmacy status, and demographics. Prescription records verified medication counts and drug-related risks. Determinants of regimen complexity were assessed using multivariable linear regression, and predictors of ADE reporting were examined using multivariable logistic regression. Among 201 participants, 101 (50.2%) reported at least one ADE in the past month. Polypharmacy, comorbidities, and multidose dispensing service use were independently associated with higher regimen complexity, whereas higher income, college education, and older age were associated with lower complexity. Higher MRCI-K scores (OR = 0.95, 95% CI 0.91-0.99) and older age (OR = 0.98, 95% CI 0.96-0.99) were associated with lower odds of ADE reporting. Higher medication regimen complexity and older age were associated with reduced reporting of ADEs, suggesting possible under-recognition among these populations. Patient-centered strategies are needed to enhance ADE identification in individuals with complex medication regimens.