I have to agree with Cece (the one right above me). If he's going to OD, he'll do it anywhere. In fact, would it not be harder to deal with if he did it while AT your house?
I think you're doing the right thing. I cannot tell you how many times I've wished my parents would have let my sister suffer her own consequences. She lives with them to this day... and it is helping no one. It has only made it easier for her to steal from them before her trips to the pawn shop.