The investigators hope to learn the efficacy of 6 weeks treatment of RO4995819 versus placebo as adjunctive therapy in patients with MDD having inadequate response to ongoing antidepressant treatment based on mean change in Montgomery Asberg Depression Rating Scale (MADRS) scores from baseline to end of treatment.~This knowledge is valuable because it is a new medication, which may have utility in the population of patients with major depressive disorder.
The purpose of the study is to explore the efficacy of 6 weeks treatment of an investigational medication, RO4995819, versus placebo as adjunctive therapy in patients with major depression.