Depression is present in 10% of patients attending primary care services and is generally not identified. In Mexico it is estimated a prevalence of 12% to 20% among adults between 18-65 years old[1]. Up to 75% of patients treated with a selective inhibitor of serotonin reuptake (SSRIs) are not responding adequately[2]. Atypical antipsychotics are an effective alternative for these patients. OBJECTIVES: To evaluate the cost-effectiveness (CE) of extended release (XR) quetiapine as adjunctive therapy (AT) in patients with major depressive disorder (MDD) that doesn’t respond to antidepressant treatment (AD), compared with other antipsychotics listed in the Mexican Formulary (aripiprazole and olanzapine). METHODS: A Markov model was developed to perform and incremental analysis with weekly cycles during eight weeks time horizon, based on the meta-analysis developed by Komossa et.al in 2010. Health states: remission, relapse and discontinuation of treatment. The model estimates the remission time gained (RG) by each AT alternative. The analysis was done from society perspective, considered direct costs, and reported in 2013 US dollars[3]. RESULTS: Patients with AT with quetiapine XR had 1.83 weeks of RG, while patients under aripiprazole and olanzapine obtained 1.5 and 1.72 weeks of RG, respectively. Quetiapine XR compared to olanzapine generated an additional cost per patient of $94.70, with additional RG of 0.11 weeks and ICER of $881.73. Quetiapine XR dominated extendedly to aripiprazole. Robustness of results were confirmed by additional deterministic and probabilistic sensitivity analysis. CONCLUSIONS: The use of quetiapine XR as adjuvant treatment for non-responders patients is a cost-effective compared to aripiprazole and olanzapine, and could be considered as an option in an institutional setting. [1] Programa de acción en salud mental. (2004). Instituto Mexicano de Psiquiatría. [2] NIMH. www.nimh.nih.gov/trials/practical/stard/index.shtml (2013). [3] Exchange rate $12.48 MXN per USD.