An Investigation of the Sleep Architecture and Consequent Cognitive Changes in Olanzapine-Treated Depressed Patients

Inclusion Criteria: 1. A diagnosis of major depressive disorder or bipolar disorder type 1, 2 or NOS by Diagnostic and Statistical Manual of Mental Disorders- Fourth Edition (DSM-IV) 2. Current depressive episode with a HAMD-17 of \> 15 3. Males or females over age18 years (yrs) 4. Inpatients or outpatients 5. Female patients of childbearing potential must be using a reliable method of contraception and have a negative urine human chorionic gonadotropin (HCG) test at enrollment 6. Able to understand and comply with the requirements of the study 7. Provision of written informed consent Exclusion Criteria: 1. Current manic, hypomanic or mixed episode, with YMRS \> 12 2. Current or past diagnosis of schizophrenia and dementia 3. Pregnant women, or women in childbearing age, not willing to use appropriate contraception or women currently nursing 4. Patient on any other antipsychotic medication 5. Patients who, in the opinion of the investigator, pose an imminent risk of suicide or a danger to self or others 6. Known intolerance or lack of response to olanzapine, as judged by the investigator 7. Benzodiazepines and all other sleep-aids must be discontinued prior to participation in the study if they have not been at a stable dosage for the 4 weeks previous to entry into the study 8. No change to the current medication regime (excluding discontinuation of sleep aids and antipsychotic medications) is allowed 4 weeks prior to the first PSG reading 9. Administration of a depot antipsychotic injection within two dosing interval (for the depot) before randomization 10. Substance or alcohol dependence at enrolment or in the last three months (except for caffeine or nicotine dependence), as defined by DSM-IV criteria 11. Serious, unstable or inadequately treated medical illness as judged by the investigator 12. History of epilepsy or uncontrolled seizures 13. Involvement in the planning and conduct of the study 14. Previous enrolment in the present study 15. Participation in another drug trial within 4 weeks prior enrolment into this study or longer in accordance with local requirements