Therefore, in the present study the investigators goal is to investigate whether quetiapine fumarate XR at a dosage of 300 mg per day has an impact on HPA axis activity in unipolar depressed patients, as measured by serial dexamethasone/CRH tests (week 0, 1, and 5) and salivary cortisol profiles and whether putative effects of quetiapine XR on the HPA system are related to its antidepressant efficacy.