Participants
TRD, psychiatric
DISORDER, DISORDERS
This study recruited adults aged 18 years or older who were outpatients and referred by practitioners from specialized psychiatric services or word of mouth from primary care services. Participants were experiencing TRD, defined by meeting the Diagnostic and Statistical Manual of Mental Disorders (5Participants were taking a locally approved therapeutic dose of a single SSRI with at least 75% adherence for a minimum of six weeks prior to taking part and were asked to continue this treatment for the duration of the study. Permitted SSRIs included citalopram, escitalopram, fluoxetine, paroxetine, sertraline, vilazodone, and vortioxetine. Participants taking multiple antidepressant therapies were excluded.Participants experiencing a major comorbid psychiatric disorder or suicide risk were excluded based on clinical assessment, medical records, the Mini International Neuropsychiatric Interview (version 7.0.2), the McLean screening instrument for borderline personality disorder, and the Columbia-Suicide Severity Rating Scale (C-SSRS) [