Dude, just be honest. Go tell your friend you’re worried about his recent drastic change in behaviour. None of the drinking vs smoking stats matter here, what matters is that you as a friend have observed a rapid change and it caused you to be concerned. I believe that every friend has the right to speak their honest mind once, after then you have said your bit and you can’t do anything else beyond let your friend live their own life and learn the consequences of their choices and actions. After all, change must come from within. Whether he chooses to return to a life of education is his choice to make. Then again, maybe he’s just someone who is willing to be stoned. I’m not “stoned all the time” but I do smoke very regularly, and I’m completely successful. Weed doesn’t necessarily exclude someone from being dedicated. Nor is weed necessarily the reason he may or may not become a psychiatrist. It becomes easy to blame one thing for people changing when in reality people change naturally over time, it’s inevitable.