Substance abuse is common in those with ADHD, often resulting from self-medicating:
If he needs the substances to get through the day, it’s probably time to start considering addiction and how to address it.
A diagnosis could come as a relief to him too:
https://www.additudemag.com/category/understand-conditions/adhd-in-adults/diagnosis-add/.
Of course, until he wants to change, nothing you do will instigate change.
Penny
ADDitude Community Moderator, Author & Mentor on Parenting ADHD, Mom to teen w/ ADHD, LDs, and autism