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

## TL;DR

This study found that more complex medication regimens and older age are linked to fewer reported adverse drug events in Korean community pharmacies.

## Contribution

The study provides new evidence on how medication regimen complexity affects patient-reported adverse drug events in a Korean community pharmacy setting.

## Key findings

- 50.2% of participants reported at least one adverse drug event in the past month.
- Higher MRCI-K scores and older age were associated with lower odds of ADE reporting.
- Polypharmacy and comorbidities were linked to higher medication regimen complexity.

## Abstract

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.