Inclusion Criteria:

• Clinical diagnosis of Pathological Gambling using the clinician-administered Structured Clinical Interview for Pathological Gambling (SCI-PG) (Grant et al., 2004);
• Gambling behavior within 2 weeks prior to enrollment;
• For women, negative results on a urine pregnancy test and stable use of a medically accepted form of contraception.

Exclusion Criteria:

• Infrequent gambling (i.e. less than one time per week) that does not meet DSM-IV criteria for PG;
• Unstable medical illness or clinically significant abnormalities on laboratory tests, EKG, or physical examination at screen;
• History of seizures;
• Myocardial infarction within 6 months;
• Current pregnancy or lactation, or inadequate contraception in women of childbearing potential;
• A need for medication other than memantine with possible psychotropic effects or unfavorable interactions;
• Clinically significant suicidality;
• Current Axis I disorder determined by the SCID and SCID-compatible modules for impulse control disorders (Grant et al., 2005), except for nicotine dependence;
• Lifetime history of bipolar disorder type I or II, dementia, schizophrenia, or any psychotic disorder determined by SCID;
• Current or recent (past 3 months) DSM-IV substance abuse or dependence;
• Positive urine drug screen at screening;
• Initiation of psychotherapy or behavior therapy within 3 months prior to study baseline;
• Previous treatment with memantine;
• Treatment with investigational medication or depot neuroleptics within 3 months, with fluoxetine within 6 weeks, or with other psychotropics within 2 weeks prior to study baseline.