The purpose of this research is to determine if patients on corticosteroids who are given memantine will show improvement in memory compared to those receiving placebo (an inactive substance). This research also seeks to determine if such patients, when given memantine, will experience improvement in manic/hypomanic symptoms (feelings of agitation, overexcitement, or hyperactivity) and/or depressive symptoms. Subjects will be randomized to a crossover trial of memantine and placebo for 8 weeks, followed by a 4 week washout and then 8 more weeks of the study medication. Memantine and placebo will start at 5 mg/day for one week, increased to 5 mg twice a day in the second week. During the third week patients will take 10 mg in the morning and 5 mg in the evening. At weeks 4-8, patients will take 10 mg twice a day. One 8 week course of study medication will be memantine and the other 8 week course of study medication will be placebo, both assigned in a random fashion.