Memantine and Cognitive Dysfunction in Bipolar Disorder

Inclusion Criteria: * Diagnostic and Statistical Manual-IV (DSM-IV) diagnostic criteria for any bipolar disorder \[type I, type II, and not otherwise specified (NOS)\] (diagnosed with the use of the Structured Clinical Interview for DSM-IV-TR Mood Module (SCID Mood Module) * Written informed consent * Men or women aged 18-65 * A baseline Hamilton-D 17 score of \< 10 at screen and baseline visits. * A baseline Young Mania Rating Scale score of \< 10 at screen and baseline visits. * No acute episodes of depression or mania for the previous 12 weeks. * Massachusetts General Hospital Cognitive and Physical Functioning Scale: Cut-off: \>15 or Everyday Cognition Self-Report Form: Average of all items \>1.5 or Repeatable Battery for the Assessment of Neuropsychological Status (RBANS): \<12 years education, RBANS total scale score of \<85 =12 years education, RBANS total scale score of \<93 \>12 years education, RBANS total scale score of \<100 * Able to read and understand English. Exclusion Criteria: Patients meeting any of the following criteria will be excluded from the study: * Participants with suicidal ideation where outpatient treatment is determined unsafe by the study clinician. These patients will be immediately referred to appropriate clinical treatment. * Pregnant women, nursing mothers, or women of childbearing potential who are not using a medically accepted means of contraception (defined as oral contraceptive pill or implant, condom, diaphragm, spermicide, intrauterine device (IUD), s/p tubal ligation, partner with vasectomy). * Serious or unstable medical illness, including liver impairment, kidney impairment, cardiovascular, hepatic, respiratory, endocrine, neurologic or hematologic disease. * History of seizure disorder, brain injury, any history of known neurological disease \[multiple sclerosis, degenerative disease such as amyotrophic lateral sclerosis (ALS), Parkinson disease and any movement disorders, etc\]. * History or current diagnosis of the following DSM-IV psychiatric illness: organic mental disorder, schizophrenia, schizoaffective disorder, delusional disorder, psychotic disorders not otherwise specified, major depressive disorder, patients with substance dependence disorders, including alcohol, active within the last 12 months. * History of multiple adverse drug reactions. * Patients with mood congruent or mood incongruent psychotic features within the last 12 months. * Clinical or laboratory evidence of hypothyroidism. * Patients who have had an episode of acute depression or mania during the 12 weeks prior to enrollment. * Patients who have had electroconvulsive therapy (ECT) within the 6 months preceding enrollment. * Patients taking drugs which alkalinize the urine.