If you are found to be eligible to take part in this study, you will be randomly assigned (as in toss of a coin) to 1 of 2 groups. Participants in Group 1 will stay on morphine only. Participants in Group 2 will receive morphine plus methadone. You will have an equal chance (50/50) of being placed in either of the 2 groups. You, the medical staff, and study researchers will not know which group you have been assigned to. If necessary, your doctor will be able to find out what group you are in the event of an emergency.