Memantine for the Treatment of Cognitive Dysfunction and Negative Symptoms in Patients With Chronic Schizophrenia

Inclusion Criteria: * Diagnosis of schizophrenia (DSM-IV) * Age 18 to 40 * Stable negative syndrome (PANSS negative score \> 20) * At least one previous schizophrenic episode * Informed consent * Subjects must be considered by the investigator to be compliant with investigations and appointments * Subjects must have an educational level and a degree of understanding such that they can meaningfully communicate with the investigator Exclusion Criteria: * Axis I disorder other than schizophrenia within 12 months, e.g. schizoaffective disorder * Severe positive symptomatology (PANNS positive score \> PANNS negative score) * Dependency on alcohol or addictive drugs within 6 months of the baseline evaluation * Contraindication of risperidone * Significant neurological, cardiovascular, hepatic, renal, metabolic, or other medical diseases or any clinically relevant abnormalities in laboratory tests