Drug use flies under the radar at UR, for the most part. People will smoke, and some do often, but students aren't constantly bombarded with its presence. You might have a neighbor who is into some extracurricular illegal activities, but for students that are not at all in the drug scene, it can be easily avoided. Marijuana is the drug of choice for UR, similar to most colleges. There is harder drug use, but this is even less prevalent.
Occasionally, drug use will become apparent; for example, when people smoke openly on 4/20 on the main quad, but that is the most obvious example of drug use on campus and not the norm. Security does enforce the policies, and if students are caught, it is dealt with accordingly. Certain people have reputations in terms of drug use, but people go about their business and generally are left to do their own thing. Each person recognizes that the other is old enough to make their own decisions about their choice of lifestyle, and as a result, people hang out with those similar to them, and it's no big deal.