House's Surprisingly Nice Attitude Due to Methadone?

Everyone was bewildered, baffled, or should I say in the highest form of confusion when House was starting to act weird.

For once, he was suddenly in a good mood as evident in his being courteous and agreeable to the parental demands of his patients. Consequently, everyone's guessing that House must be high on drugs. He is said to have taken methadone that makes him able to walk without a cane.
Wilson even convinces Cuddy into letting House maintain the methadone and so keep his job, which is just amusingly foolish.

Seriously what is a methadone? How does it work?

According to wikipedia, there are a lot of forms of methadone such as Symoron, Dolophine, Amidone, Methadose, Physeptone, Heptadon and many others. This is a synthetic opioid, prescribed as an analgesic, antitussive and a maintenance anti-addictive for use in patients on opioids.