<qa>  How many eligible patients will be enrolled in a randomized, double-blind,A randomized, double-blind, placebo-controlled, add-on study of lamotrigine in trigeminal neuralgia. Thirty-eight eligible patients with trigeminal neuralgia will be enrolled; nineteen will be randomized to the active medication group and nineteen to the placebo group. Using a daily diary, all patients will document their overall pain level and attack frequency and intensity for four weeks. After the four week baseline period, patients will initiate medication lamotrigine or placebo. Patients will titrate until either they reach the maximum dose of 400mg per day and up to 700mg for patients on enzyme-inducing anti-epileptic drugs EIAEDs, their side effects inhibit further increases known as maximum tolerated dose MTD, or their trigeminal neuralgia pain resolves referred to as pain free dose PFD over eight weeks. Patients will remain on a constant dose of prior medications throughout the study. Patients will remain on maximum dose, MTD, or PFD for a maintenance period of at least eight weeks, and at the end of the maintenance period patients who opt to stay on the medication will be unblinded as to medication and dosage. Primary outcome will be average intensity of daily pain. 