MARIGOLD Study: A Study of RO4917523 Versus Placebo as Adjunctive Therapy in Patients With Major Depressive Disorder and an Inadequate Response to Ongoing Antidepressant Therapy

Inclusion Criteria: * Adult patient, 18 to 70 years of age at time of informed consent * Major depressive disorder without psychotic features as defined by DSM-IV-TR criteria * Inadequate response to ongoing antidepressant treatment, as defined by protocol * Body mass index (BMI) 18 to 38 kg/m2 inclusive Exclusion Criteria: * Currently receiving treatment with a combination of antidepressants (two or more), or an adjunctive potentiating treatment as defined by protocol * Previously received RO4917523 * History of failure, or utilization during the current episode of Electroconvulsive Therapy (ECT) or repetitive Transcranial Magnetic Stimulation (rTMS) * History of use at any time of Vagus Nerve Stimulation (VNS) or Deep Brain Stimulation (DBS) * Current or past history of bipolar disorder (e.g. manic, hypomanic, or mixed episodes) * Pregnant or lactating women