6. Concurrent treatment with acetylcholinesterase inhibitors, antipsychotic agents, mood stabilizers (valproate or lithium) or benzodiazepines (other than temazepam or zolpidem), or use of any of these agents within 4 weeks prior to randomization. Atypical antipsychotic agents may be started after the baseline visit if felt to be medically necessary by the investigator and will be recorded as a secondary outcome measure.