Retrospective Observational Study DIANA Study

Inclusion Criteria: 1\. Female or male aged between 18 and 65 years Inpatients and outpatients diagnosed with an episode of major depression relating to RDD (ICD-10, Version 2010) during the period from January 1, 2012 till September 30, 2013 3. Initially treated with antidepressant monotherapy, using a flexible dosage regimen if required, for at least 2 weeks 4. Initial treatment changed because of a suboptimal response at physician's discretion, which is clearly documented in the patient's medical chart. Exclusion Criteria: Patients currently participating in any other clinical or non-interventional trial, or have completed their participation with the last 30 days. 2\. Patients with current psychiatric or general medical conditions which require concomitant use of lithium, thyroid hormones, or atypical antipsychotics 3. Patients with unstable general medical condition. 4. Patients who were pregnant or were suspected to be pregnant during the period when a patient had received treatment for MDE (Major Depressive Episode).