The main drug in use on campus is marijuana. Stimulants are also fairly common during exams. RPI is not much different from most campuses in this respect. Most students prefer alcohol, with marijuana coming in a distant second. Overall, the campus has very few problems; even the number of reported incidents is low, considering the size of the campus.
Basically, any drug scene at RPI is limited to those who want to be in it. There is no pressure to do anything if you don't want to, and those groups that choose to use drugs mainly stick to themselves. It's important to remember that there are drugs out there. If you don't want them, however, you could probably go through four years and never see a thing.