If he's on methadone it can cause similar symptoms to any other opiate. Support him in his journey to get clean. Until he is clean from opiates for months he could be unstable, depressed, moody, not hungry. I've taken methadone and it made me feel like all that and took months to feel myself after stoping... and still went back to using. Addiction never goes away, and who he hangs out with has a lot to do with his success.