The study design will have three overlapping phases that are summarized below: 1) A one week methadone fixed induction (week 1) and flexible stabilization phase (weeks 2-9); 2) an 8-week "treatment" phase (weeks 2-9), consisting of slow titration and stabilization on study medication; and 3) a four week "taper, detoxification or transfer" phase (weeks 9-12).