Methadone hampers the digestive system. It doesn't allow your digestive tract to take in nutrients properly. Eat alot of fresh veggies and fruit. Take plenty of vitamins and supplements. This may help. You have lost a dangerous amount of weight. Go to a different Doc. I have been on Methadone for 18 months am in day 5 of being clean. Good luck.
I would go and see a doctor ASAP. That is way to much weight to have lost.