Hey alpinyata and welcome to Bluelight. There are certainly some people here with with wisdom and experience on this. I you feal comfortable please share what and how much you're using and for how long you have been at it. This will help people give you better advice. I was on methadone for a while and I would combine it with a vitamine D supplement for sure and if you are male I would have your testosterone levels checked frequently.
Also methadone is very hard and unpleasant to get off of once a person has a high dose or has been on it for a long time. Its a full opiate agonist pluss a NMDA agonist pluss a serotonin and epinephrine reuptake inhibitor. Neuropathic Pain: Causes, Management and Understanding
So with this level of manipulation getting of of it can be burly to say the least.
I am certainly not trying to dissuade you from getting on methadone. I'm just makeing sure you are aware of some things so you can make an informed choice to promote the best possible outcome.
There is also some good information on post 2 of this thread, there is also a bupe DR locator as well.