family

Aside from a family intervention and forcing him to AA meetings, or catching him out doing something illegal and making sure he gets caught (Drink driving for example) there's not a lot you can do about it. It's his life, and as much as you don't agree with it, he's made the decision to drink himself, and he won't stop just because you want him to. Talk to him, sit him down and tell him your fears and see what he says. You can't force him to quit. He'll need to want to himself, otherwise every time he's forced to stop, he'll go straight back to it. Good luck.