OBJECTIVES: To describe and compare treatment patterns and health care costs in patients with depression initiating treatment with antidepressant (AD) (in monotherapy or in combination) and patients initiating AD treatment combined with benzodiazepine (BZD) using claims database in Japan. METHODS: Using data from the Japan Medical Data Center (JMDC) database, a retrospective longitudinal cohort study was conducted, including adults aged 18-65 years with a first prescription of AD (index date) between January 2009 and September 2013, and diagnosed with major depression around index date. Time to treatment discontinuation (gap of 90 days without AD treatment) and total costs at 6 and 12 months were estimated for each group (AD vs. AD+BZD), and compared, with adjustment on potential confounders (gender, age, insurance status, index year and baseline costs) using Cox proportional-hazards regression and log-linear regression models.  RESULTS: