 On the day of admission or inclusion in the study day 1, all subjects fulfilling the eligibility criteria and enrolled in the study will be allocated by 1:1 randomization to two groups, using a centralized telephone-based randomization office located at the coordinating institution and stratification to ensure that the proportion of patients receiving a brand or a generic at baseline is comparable between groups. For subjects taking concomitantly more than one AEDs being tested, separate randomizations will be conducted separately for each AED for example, a subject receiving valproic acid and carbamazepine will be randomized to continue on the same formulation of valproic or to switch to a different formulation of valproic acid, and at the same time separately randomized to continue on the same formulation of carbamazepine or to switch to a different formulation of carbamazepine. 