 - To determine whether methadone used as first line strong opioid is superior to morphine as evidenced by reduced frequency of neurotoxicity, dose escalation and treatment failure over a 12-week treatment period. Previous studies have demonstrated that patients develop increased pain or neurotoxicity after chronic use of morphine and require frequent opioid escalation. Researchers postulate that methadone will demonstrate lower opioid induced neurotoxicity, less frequent dose escalation and less treatment failure over 12-week treatment period as compared to morphine. 