Analyses will be conducted on both intent-to-treat and per-protocol. Any subject who is valuable for the safety analysis that also has baseline and end of drug treatment period neuropsychological data available for each of the two drug periods will be evaluated for the intent-to-treat analyses of the parameters of interest. Mood and neuropsychological data will undergo analysis of variance (MANOVA) appropriate for a two-period crossover study. Alternative forms will be used when available. To compensate for practice effects and evaluate for measurement error, baseline will be defined as the average of the evaluations conducted at pre-treatment baseline and the post-treatment period (week 12).18 Subjects who discontinue prematurely will be tested two weeks after withdrawing. This will be considered the post-treatment period for these subjects.