 Patients will be randomized to receive tablets of either placebo or topiramate in a double-blind, crossover design using randomization tables. Following the completion of the first arm of the study and the tapering and washout phases, patients will receive topiramate or placebo in a crossover design for the same treatment duration. The dose of topiramate will be slowly escalated twice each week as tolerated. If a patient cannot tolerate a higher dose, the dose will be reduced to the previously tolerated dose. 