Study selection and appraisal of studies were performed independently by two researchers (SW and SR). Disagreement was resolved by consensus. Information was extracted via a standardized checklist included study design, duration of the study, comparability of study groups with respect to sex, age, baseline scores of cognitive, psychopathological and activities of daily living scales and clinical outcomes on different rating scales in the following domains: cognition, activities of daily living (ADLs), neuropsychiatric symptoms, patients' quality of life, response according to the studies' definitions and drop out rates due to side effects. The study and publication quality was assessed on the basis of whether the following quality criteria had been adequately fulfilled: randomization and allocation concealment, blinding of patients and investigators, sample size estimation, handling and