Treatment Interrupts Depression Early

Inclusion Criteria: * Age 12-25 years * Diagnosis of major depressive disorder, onset of the major depressive disorder within the last 12 months. Depression considered the most significant problem in need of treatment. * An additional inclusion criterion for entering Stage 1 (active intervention) is a minimum moderate depression severity (CDRS-R≥40; MADRS≥20) that justifies the need for treatment. Individuals who fulfill general inclusion criteria but are below the depression severity threshold for active intervention will still be eligible to participate in follow-up assessments. * Verbal ability sufficient to participate in psychological treatment. Exclusion Criteria: * Personal history of a manic or hypomanic episode, diagnosis of a psychotic disorder, pervasive developmental disorder or autism spectrum disorder, intellectual disability, mental disorders secondary to neurological or other medical condition, active substance use disorder. * Previous trial of any treatment for major depressive disorder lasting 4 weeks or longer, current use of antipsychotic, antidepressant or mood-stabilizer medication. * Recent (past 6 weeks) change in any psychotropic medication (including stimulants, hypnotics, anxiolytics) or receipt of 4 of more sessions of cognitive-behavioural therapy. * Pregnancy or breastfeeding. If participants become pregnant or learn of pregnancies during the study, we will consult with Dr. Tanya Tulipan and jointly make the best decision for the participant with the option to either continue or end study treatment. * No one will be excluded based on sex, gender, race, ethnicity, or living arrangements.