Intervention: Patients are randomized to carbamazepine, gabapentin or lamotrigine. Target doses are 600mg for carbamazepine (200mg tablets overencapsulated), 1500mg for gabapentin (300mg capsules), and 150mg for lamotrigine (25mg tablets). Carbamazepine and gabapentin patients also receive a placebo tablet while lamotrigine patients also receive a placebo capsule.