This is a double-blind, placebo-controlled trial of the effects of memantine in adult epilepsy patients. Patients will be assessed for neurocognitive outcomes, seizure frequency and side effects. After a two-month prospective baseline during which seizure frequency and neurocognitive parameters are documented, patients will be randomized to either memantine or placebo and evaluated after twelve months on study drug. The treatment period will consist of a one month dose escalation phase, followed by an eleven month maintenance phase. The dose escalation is 5 mg in PM for days 1-7, 5 mg twice daily for days 8-14, 5 mg in AM and 10 mg in PM for days 15-21 and 10 mg twice daily from day 22 and continue. The neuropsychological battery performed during baseline will be repeated at the end of the twelve month treatment period. No special procedures are required for this study, except the neuropsychological testing, which is not a routinely performed evaluation for adult epilepsy outpatients.