For safety focus on the methadone. I assume that is for a chronic pain condition?
Methadone can be tricky. If the patient ever passes out and can not be awakened, it might be a methadone overdose and patient needs the antidote. (I always wished I had a life alert alarm that would alert me if someone stopped breathing so I could quickly react and save them.)
There are new ways of treating certain types of chronic pain, especially if patient has physically recovered but still feels pain. See book chapter 1 of Norman Doidge, M.D. The Brain's Way of Healing (his 2015 book, I think that is the title.)
A question to ask is, how mentally alert is your Dad? Does he have any cognitive impairment, such as Alzheimer's? Is he in a nursing home or living on his own or with family? The answer depends partly on that, because psychiatrists and doctors treating the elderly in a confinement setting will often just try out passels of drugs on people just to get them to be quiet and cooperative. This particular drug is very stimulating for most people, which can potentially partially counter-act the narcotic effects of the methadone. Safety is a very complex issue; it doesn't just involve normal contraindications, it also involves how any medication affects a particular person as we respond differently to them. I'm assuming some professional has decided your Dad is depressed. Is he? Is he possibly over-medicated on the Methadone, which would cause depression? Which is why how mentally alert he is has importance, as it determines how well he is advocating for himself and describing what he's feeling.