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

Introduction Major 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.