Clinical efficacy, safety and applicability of home-based bright light therapy in outpatient adolescents with major depressive disorder in China: protocol for a randomised controlled trial.

introductionMajor depressive disorder (MDD) is a leading cause of disability among adolescents, yet available treatments remain limited. Bright light therapy (BLT) is a non-pharmacological intervention with demonstrated efficacy in adults. However, its clinical utility and underlying neural mechanisms in adolescents remain unclear. This trial aims to evaluate the clinical efficacy, time to onset, safety and applicability of home-based BLT in outpatient adolescents with MDD, and to explore its underlying neural mechanisms using functional near-infrared spectroscopy (fNIRS). METHODS AND ANALYSIS: This is a randomised, placebo-controlled, three-arm multicentre clinical trial. A total of 126 outpatient adolescents aged 13-17 years with MDD will be randomly assigned to receive high-intensity BLT, medium-intensity BLT or placebo dim red light using a portable light box in a home-based setting for 40 min each morning over 4 weeks, followed by a 2-week follow-up. 42 age-matched and gender-matched healthy controls will also be enrolled for baseline assessments only, serving as normative references for comparison. The primary outcome will be the change in total scores on the 17-item Hamilton Rating Scale for Depression from baseline to week 4. All analyses will follow an intention-to-treat framework to ensure methodological rigour. The primary outcome will be analysed using analysis of covariance and linear mixed-effects models. Secondary outcomes will include response and remission rates, time to onset, maintenance of efficacy, self-reported depressive symptoms, sleep quality, cognitive function, anxiety, irritability, suicidal ideation, non-suicidal self-injury, self-efficacy and the overall safety profile of BLT. Prefrontal cortical activity will be measured using fNIRS at baseline and week 4 to explore potential neural mechanisms. Approximately 15% of participants will additionally take part in a qualitative substudy exploring experiences and acceptability of BLT. ETHICS AND DISSEMINATION: The study protocol has been approved by the Ethics Committee of Peking University Sixth Hospital (approval number: 2025-24). Written informed consent will be obtained from all participants and their legal guardians prior to enrolment. Study findings will be disseminated through peer-reviewed journals and conference presentations. TRIAL REGISTRATION NUMBER: NCT06913309.