The subjects will be examined before and after four weeks of treatment by a thorough interview concerning psychiatric symptoms (SCAN), including depressive symptoms, personality, perceived stress and cognitive function. The effect of antidepressant on stress is measured with saliva-cortisol and by the response to the combined dexamethasone corticotropin-releasing (CRH) hormone test. Additionally, MR and PET scans of the 5-HT4 receptor function will be conducted before and after 4 weeks of treatment.