We aimed to evaluate the prevalence of potentially inappropriate medication (PIM) use and drug-drug interactions (DDIs) in older adults and their associated factors. This cross-sectional study used National Health Insurance data of older adults in South Korea. The 2015 AGS Beers Criteria were used to classify PIM use and DDIs. The associations of PIM use and DDIs with patient- and prescriber-related factors were evaluated using multiple logistic regression. Of the older adults who received at least one outpatient prescription ( = 1,277,289), 73.0% and 13.3% received one or more prescriptions associated with PIM use or DDIs, respectively. Chlorphenamine was most commonly associated with PIM, followed by diazepam. Co-prescriptions of corticosteroids and NSAIDs accounted for 82.8% of DDIs. Polypharmacy and mainly visiting surgeons or neurologists/psychiatrists were associated with a higher likelihood of prescriptions associated with PIM use or DDIs. Older age, high continuity of care (COC), and mainly visiting a hospital were associated with a lower likelihood of PIM use or DDIs. Prescriptions associated with PIM use and DDIS were more frequent for low COC patients or those who mainly visited clinics; therefore, patients with these characteristics are preferred intervention targets for reducing prescriptions associated with PIM use and DDIs.