Aim
　  To determine the impact of increased copayment on long-term care (LTC) and medical service utilization among older adults in Japan.
Methods
　  LTC and medical claims data were obtained for individuals aged ≥ 75 years as of August 1, 2014, and those utilizing LTC services in Fukuoka Prefecture, Japan, between August 2014 and March 2019. Participants were categorized into three groups: the 10% group (no copayment change), the 20% group (copayment increased from 10% to 20% in August 2015), and the 30% group (copayment increased from 20% to 30% in August 2018). Monthly panel data was constructed , and controlled interrupted time series analysis was used to estimate changes in LTC and medical expenditures before and after the copayment increases.
Results
　  Of 32,295 participants, 2991, 1459, and 925 were in the 10%, 20%, and 30% groups, respectively. LTC expenditure increased significantly by an average of 502.5 yen per month during the 12 months before the first intervention, with a further significant increase of 560.0 yen between the two intervention periods. The 30% group had a significant decrease (569.9 yen/month) in facility service expenditures and a significant increase (996.5 yen/month) in hospitalization expenditures after the second intervention. Conclusions
　  No clear reduction in LTC expenditure was observed, suggesting a possible shift from LTC to medical care. Further research is needed to examine measures, including copayments, for the appropriate medical care and LTC service use.