You have to do all that you can to get him out of it.
Yukti (skill), shakti (strength), priti (love); with love, skill and through some force, somehow, you must help him to get out of it.
The best thing is to put them in a rehabilitation home. There are many other rehabilitation centers all over. Take him to such a center, make him do the Sudarshan Kriya. If he learns the kriya and pranayama, it makes a big difference. Many people have left drugs and alcohol when practicing the Sudarshan Kriya.