I can't really comment much since I've never had to deal with an issue anywhere close to this, but as a random thought, isn't this something his family would ideally action on? To me it seems great that you are helping him by not allowing him to drive, etc. especially if he is a nice person, but I would think that this might be a a little off your reach. I'm definitely not trying to discourage you but at least where…
As someone who once had an experience with a coworker who was suffering with addiction / mental health issues, I agree with this comment entirely. While it's admirable to want to help as much as you can, I learned the hard way that it would have been better to simply alert family to my concerns and then step away.