You DID all you can now all you can do is let him know you love him and have a very serious conversation about what he is doing to himself. The dangers of the pill combination. How they can and do cause seizures leading to early death. Ask him why he wants to self destruct himself. I knew a guy that mixed pills and started with strokes, had a few heart attacks by the time he was in his mid 30's and was dead by 40.
Pill combinations are serious but your hands are pretty much tied if he is persistent in doing what he is going to do. He has to want help. He doesn't see he has a problem to want help.
I don't know if tough love of kicking him out and selling your house would work or drive him further into his ways.
He needs help but he has to WANT help.
Is he being drug tested by his PO?