This study is being done to find the optimal dose of methadone (a long acting pain medication) that decreases the amount of pain that people have after spine surgery. Five different doses of methadone will be compared to each other, while keeping the remainder of the anesthetic routine for surgery. The investigators will determine the analgesic dose-response of methadone. The investigators will also determine the effect of methadone on the incidence of opioid related side effects, the quality of outcome of recovery, and the change in the 3-month opioid use.
