Starting on week 2 subjects will start study medication in one of two randomly assigned experimental groups: levetiracetam 3000 mg /day (active medication) or placebo (inactive medication). Concurrent with the stabilization on methadone, levetiracetam will be increased from 500mg/day on week 2 and this dose will be slowly titrated to a total of 3000mg/day or maximum tolerated dose (MTD). Subjects will remain on their full dosage through week 13.