Sorry if I am being ignorant, but is this slightly different in that your father was originally prescribed pain medication for a painful condition rather than just abusing drugs?
Is he still in a lot of pain from his original condition and does that ned to be addressed before he stops all the pills and potions?
There is often a lot misunderstood when pain medication is prescribed and often tolerance can occur and pseudo-addiction. Pseudo addiction occurs when a patient is not sure where or when there next supply is coming from. However a lot of medical practioners are scared by this and confuse it with real addiction, which it is not. They then stop the supply of tablets which leads to addictive behaviours in terms of searching for supplies and buying illegally. However if the patient knows where and when the supply will come from, those behaviours should stop.
Does your Dad have a pain management doctor who is helping him with this?
I hope I am not intruding where I am not wanted.
Best to you
B
x