Quitting drugs is only the first step. It takes over a year of constant therapy to get better. It also matter what age he started using drugs cause they become stuck at that age until they stop using. If indeed he also has an mental illness he still needs treatment.
You did the right thing whether or not he was using he needed to know his behavior was not ok and you will hold him responsible and not enable his bad behavior.
For him there is AA, NA and therapy with someone who has background in chemical abuse. For you there's Al-Anon and therapy. The whole family needs help to deal with it. Best of luck.