A parallel-group randomized controlled trial of a culturally adapted, rumination-focused cognitive-behavioral therapy (RFCBT) guided self-help targeting repetitive negative thoughts in Japanese female university students – study protocol for the RESU

Female university students face an elevated risk of developing common mental health problems, including depression and anxiety. Rumination, a specific form of repetitive negative thought (RNT), is a well-documented risk factor for these conditions. Rumination-focused cognitive-behavioral therapy (RFCBT) represents a promising intervention for the prevention and treatment of depression and anxiety, fostering mental well-being during young adulthood. Although RFCBT has demonstrated effectiveness in numerous randomized controlled trials (RCTs), cultural adaptation has emerged as a critical consideration. This study aims to evaluate the effectiveness of a culturally adapted, guided RFCBT self-help intervention in reducing RNT as well as symptoms of depression and anxiety among Japanese female university students, employing an RCT design. This study is a single-site, assessor-blinded, parallel-group, two-arm randomized controlled trial (guided self-help vs. waitlist), employing block randomization in a 1:1 ratio. A total of 102 female university students with elevated levels of RNT will be recruited. Participants will be randomly assigned to either the intervention group receiving guided RFCBT self-help, or the waitlist control group. The primary outcome is rumination, assessed using the Ruminative Responses Scale. Measurements will be conducted at 4- and 8-week post-randomization. Empirical evidence regarding the effectiveness of culturally adapted RFCBT in mitigating RNT and symptoms of depression and anxiety among East Asian populations remains scarce. If proven effective, this study will provide empirical evidence supporting the effectiveness of RFCBT in reducing RNT, depression, and anxiety within an East Asian population. Japan Registry of Clinical Trials (jRCT): jRCT1050240305, registered 27 March, 2025. (Initially registered with UMIN-CTR: UMIN000053430, on 24 January, 2024. Prospectively registered. Later transferred to jRCT.) Ver. 1.3, February 9th 2026.