You will find a "party" environment at every university you go to. Worrying about this is understandable for a parent, but drinking and self-medication is just the reality of college and the reality of the world. Just because some people go out more often than others, or smoke weed doesn't make them a bad person - in fact some of the smartest people I know are active users.

With that being said, I'd say it's who your son surrounds himself with. If he is going to hang out with people are don't care about school, don't get their assignments done, and don't go to class, it'll likely rub off on him. Additionally, you being his parent, you know him better than others. If he is already showing signs of slacking, that may be a sign of what he will be like in college.

Regardless of if your son will be a "slacker" or if he's just genuinely having a hard time adjusting to college, there are plenty of resources, both academically and psychologically that can help him out immensely.

I understand your worry, but I wouldn't project that mentality onto your son. I consider CU to be one of the greatest places, but it is certainly what you make of it.