Impact of Depression Onset and Treatment on the Trend of Annual Medical Costs in Japan: An Exploratory, Descriptive Analysis of Employer-Based Health Insurance Claims Data

We aimed to clarify medical expenses in Japanese individuals before and after major depressive disorder (MDD) diagnosis, and to determine whether MDD treatment also reduces medical costs for comorbid physical conditions. This was an exploratory, descriptive, retrospective analysis of insurance claims data from JMDC Inc. Cohort A included individuals aged 18–64 years between January 2015 and December 2019. Cohorts B and C included Cohort A individuals with diabetes/hypertension (‘chronic disease’), and sleep/anxiety disorders (‘high depression risk’), respectively. Individuals in Cohorts A–C with an MDD diagnosis were analyzed by year of MDD onset (Cohorts A–CMDD2015–2019). Diagnoses and median medical costs were derived from International Classification of Diseases 10 codes. Total medical and non-neuropsychiatric drug costs in MDD onset years were 170,390–182,120 and 8480–9586 yen higher, respectively, for Cohorts AMDD2015–2019 than for Cohort A. In Cohort AMDD2019, total medical and non-neuropsychiatric drug costs increased incrementally from 2015 to 2019 (total changes: + 165,130 and + 7365 yen, respectively), to a greater degree than in Cohort A (+ 10,510 and −1246 yen, respectively). Neuropsychiatric drug costs increased in the year of MDD onset only and decreased thereafter. After MDD onset, decreases in total medical and non-neuropsychiatric drug costs were observed (Cohorts AMDD2015–2019). Non-neuropsychiatric drug costs also decreased after MDD onset in the chronic disease groups (Cohorts CMDD2015–2019), but not in patients with MDD recurrence. Treating MDD reduces medical costs for comorbid physical conditions and may be a useful strategy for improving healthcare efficiency in Japan.