Methadone, like oxycodone, is a narcotic; most people in general develop a tolerance to narcotics taken on a long term basis, so it is very likely this will eventually happen in your case. It s difficult to predict how long this will take or be absolutely certain it will happen to you. Usually this is counteracted by increasing the dose of the drug when tolerance reduces its effectiveness. The concern with this of course is the problem of addiction. Have you tried the dopamine agonists, such as pramipexole or ropinirole? These may provide relief if the methadone eventually fails to work. Although, narcotics are usually used as a last resort for treatment of RLS after everything else has been tried. If you have pretty much tried everything else, the only option might be to increase the dose of methadone as your tolerance develops. Hope this helps.