 Study design: Sixty four 64 patients, aged 45 to 75 years, will be enrolled in the study for a period of 12 months clinical inclusion criteria are defined based on the Lund and Manchester group consensus statement revised version 1998, and followed up for 1 year in a controlled study. At the time of inclusion, the Mini Mental Status Examination MMSE score should be at least 19 below 18, a neuropsychological examination is impossible. Patients will either take memantine, or a placebo randomization ratio of 1:1 twice a day i.e., 20 mg of memantine per day in the memantine arm. The primary efficacy variable will be a global assessment tool, the CIBIC-Plus Clinicians Interview-Based Impression of Change Plus Caregiver Input. Secondary efficacy variables will include behavioral scales the NeuroPsychiatric Inventory NPI, the Frontal Behavior Inventory FBI, cognitive scales the Mattis Dementia Rating Scale MDRS, the MMSE, activities of daily living Disability Assessment for Dementia, DAD, time spent by the caregiver of the patient Resource Utilization in Dementia, RUD, and caregiver burden scale Zarit Burden Inventory, and tolerability of the drug. The main analysis will be carried out on an intention-to-treat basis in all randomized patients having undergone at least one evaluation after inclusion the Last Observation Carried Forward LOCF value, will be attributed to missing values. This analysis will be carried out at the end of the double-blind study main judgement criterion 