Dose-finding Study With Lu AA24530 in Major Depressive Disorder

Inclusion Criteria: * Major Depressive Episode that has lasted at least 3 months * Moderate to severe depression Exclusion Criteria: * Any current psychiatric disorder established as the principal diagnosis other than MDD as defined in the DSM-IV-TR and as assessed with the Mini-International Neuropsychiatric Interview (MINI) * Current or past history of: manic or hypomanic episode, schizophrenia or any other psychotic disorder, including major depression with psychotic features, mental retardation, organic mental disorders, or mental disorders due to a general medical condition as defined in the DSM-IV-TR * Major Depressive Episode that has been unresponsive to two adequate courses of antidepressant treatment, each of at least 6 weeks duration * Electroconvulsive therapy within 6 months prior to Baseline * Ongoing formal cognitive or behavioural therapy, systematic psychotherapy, or plans to initiate such therapy during the study * Clinically significant unstable illness, for example, hepatic or renal insufficiency, or a cardiovascular, pulmonary, gastrointestinal, endocrine, neurological, infectious, neoplastic, or metabolic disturbance * The patient is pregnant or breast-feeding