More than anything you should just offer your support. He doesn't NEED the substances to feel better, and becoming dependant upon them for relaxation isn't a good idea.
With that said though, it's probably a mistake better left to be made by him. Do your best to make sure that he knows he doesn't need them, but don't become preachy, that would be my best advice. Be there for him, but do not judge or look down upon him for turning to something else to help him. Not all of us are strong enough to deal with our emotions by ourselves. Just my 2c.
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