This randomized, double-blind, sham-controlled pilot trial will evaluate the efficacy and safety of transcranial alternating current stimulation (tACS) combined with sertraline in adolescents with first-episode, drug-naive major depressive disorder (MDD). Eligible participants are aged 12-18 years, meet DSM-5 criteria for a current depressive episode confirmed by K-SADS-PL, have a CDRS-R score ≥40, and have not received antidepressant treatment during the current episode.A total of 30 participants will be randomized 1:1 to receive either active tACS or sham stimulation, in addition to oral sertraline (25 mg/day in the first week, titrated to 50 mg/day thereafter). The active group will undergo 20 sessions over 4 weeks (5 sessions per week) using the NEXALIN ADI device (77.5 Hz, 15 mA, 40 minutes per session). The sham device is identical in appearance but delivers no current. Both participants and operators will remain blinded.Primary outcomes are changes in depressive symptoms, measured by the CDRS-R and BDI. Secondary outcomes include anxiety (SCARED, HAMA), global improvement (CGI-S, CGI-I), mania symptoms (YMRS), suicide risk (C-SSRS), quality of life (PedsQL4.0), sleep (PSQI), rumination (RSS), and cognition (THINC-it). Safety will be monitored through adverse events, vital signs, laboratory tests, and tolerability assessments.This pilot study will provide preliminary evidence on the potential of tACS as an adjunctive treatment for adolescent depression and inform future large-scale trials.
