Hi & Welcome!
Methadone is a very synthetic med used for pain or addiction. It does the same thing as far as blocking all the pain receptors, like the other opiates. Like all opiates of any kind they change the body and the Chemical makeup of the Brain.
If he goes everyday to pick his daily dose up, then it sounds like he is under some Dr for other Addiction. They will use Methadone or Subs these days for a maintenance program to come clean. How long, is up to the DR.
It can change your behaviors, because of the changes that goes on in the brain.
I was on Methadone for pain that was prescribed for around 12yrs when the others opiates did not work. This is because Methadone should last up to 8-12 hours for pain. I did become VERY addicted to it and was taking 2 other meds with it. Went c/t back in 2012. We do build up a tolernce and need more to do the trick, however in his case he might be serious about coming clean and this is just a tool for him right now. These are questions YOU should ask HIM about. Some ppl can nod out on Methadone, where others get wired/buzzed up. Yes, Methadone is highly Addicting too!
Methadone can suppress the respiratory more then the other opiates too.
There is not much you can do to help him, as he has to want to help himself. If he is working on coming clean then he needs all the support he can get. Going to AA/NA or any outside Support groups would help. YOU need to find out the "whys" he in on it. Please keep us updated with more info. This group is here to help ppl come clean from Addiction and to help them work on staying clean. We have all kinds of tips to help if one goes through with draws. HE is welcome to join and pick up alot of info around here. Hope you come back or he comes in.
Congratulations to YOU too for beating your Addiction, before it got the best of YOU!