Hi ya
There’s not a lot else you can do, unfortunately. The person has to recognise they have a problem and want to stop taking it and seek help to do so.
It sounds if he isn’t actively looking to stop. Until he is ready to do so, it’s like banging your head against a brick wall.
The best thing you could suggest is he get himself to CA meetings or similar. If he truly wants to stop then he will take steps to do so or ask others for help.
Stay strong.