OBJECTIVES: To determine cost-effectiveness of antidepressant groups (SNRIs, SSRIs, and TCAs) in treating major depressive disorder (MDD) over a 6-month time horizon from the viewpoint of the Brazilian Ministry of Health. METHODS: An existing decision tree model developed by our group was adapted to Brazil, based on Brazilian treatment guidelines. Clinical data were obtained from a published meta-analysis of remission rates published by Machado et al. Patients included adults >=18 with MDD, diagnosed using DSM-III/IV or comparable, with moderate-to-severe disease (HAMD>=15 or MADRS>=18), without comorbidities or comedications, and followed by >=6 weeks of treatment. Treatments included: SNRIs (venlafaxine, duloxetine, milnacipran), SSRIs (citalopram, escitalopram, fluoxetine, paroxetine, sertraline) and/or TCAs (clomipramine, amitriptyline, nortriptyline, imipramine). SSRIs were used as secondary treatment for SNRIs and TCAs, TCAs were used as secondary treatment for SSRIs. Clinical outcome was remission, defined as a final HAMD score