The purpose of this study is to determine whether mirtazapine is effective in the treatment of sleep disorders in Alzheimers disease.

Mirtazapine has been used for depressed elderly with sleep disorders with good tolerability and efficacy. The study hypothesis is that mirtazapine could also be used in demented with sleep disorders.

Sleep disorders (SD) affects 35 to 50 percent of patients with Alzheimer Disease (AD). These disorders often make caring for patients at home very difficult and It's also associated with higher risk of institutionalization and increases health care costs. Treatment of SD in people with dementia may benefit both patients and their caregivers. However, little is known about the efficacy of pharmacological treatments for treating sleep disturbances in AD.

Inclusion Criteria:

Fifty-five years of age or older; Diagnosis of probable Alzheimer's disease by National Institute of Neurological and Communicative Disorders and Stroke/the Alzheimer's Disease and Related Disorders Association criteria; Hachinski Ischemia Scale score less than 5 Mini-Mental State Examination score of O to 26 Actigraph evidence of a mean time immobile of less than 7 hours per night based on at least 7 nights of complete actigraph data collected over a single week; For-week history of sleep disorder behaviors, occurring at least once weekly, as reported by the caregiver using the Neuropsychiatric Inventory (NPI) Nighttime Behavior scale; Sleep disturbance observed was not present before the diagnosis of AD; Other co-morbidities, especially delirium, depression, chronic pain and medication use may be present, but do not cooperate in the primary symptoms; Computed tomography or magnetic resonance imaging since the onset of memory problems showing no more than 1 lacunar infarct in a nonstrategic area and no clinical events suggestive of stroke or other intracranial disease or normal; Stable medications for 4 weeks prior to the screening visit; Having a mobile upper extremity to which to attach an actigraph; Residing with a responsible spouse, family member, or professional caregiver who is present during the night and would agree to assume the role of the principal caregiver for the 3-week protocol; Ability to ingest oral medication and participate in all scheduled evaluations

Exclusion Criteria:

Sleep disturbance associated with an acute illness, delirium or psychiatric disease; Clinically significant movement disorder, such as akinesia, that would affect actigraphic differentiation of sleep and wakefulness Severe agitation; Unstable medical condition; Discontinuation of psychotropic or sleep medications within 2 weeks of the screening visit; Patient unwilling to maintain caffeine abstinence after 2:00 PM for the duration of the protocol; Patient unwilling to comply with the maximum limit of 2 alcoholic drinks per day, and only 1 alcoholic drink after 6:00 PM for the duration of the protocol; Prior use of mirtazapine for the treatment of sleep disturbances; Caregiver deemed too unreliable to supervise the wearing of the actigraph, to administer trazodone the proper time, to maintain tbe sleep diary, or to bring the patient to the scheduled visits;