 If you are found to be eligible to take part in this study, you will be randomly assigned as in the toss of the coin to 1 of 2 treatment groups. Group 1 will receive morphine while on-study. Group 2 will receive methadone. You will have an equal chance of being placed in either group. Neither you nor any of the study staff will know which study drug you are receiving. However, if needed for your safety, the study staff and study doctor will be able to find out which study drug you are receiving. 