The police will not tolerate drugs or underage drinking on campus, so if you get caught, you will be in trouble—fined, sentenced to probation, kicked off campus, or worse. The key, as students often point out, is to not get caught. There are no serious crackdowns on drugs or alcohol and no random searches, so you have to do something fairly obvious to get caught.
Get to know your RA; some are lenient and will let drinking in the dorms slide, some are much more strict and play everything by the book. If the RA finds something suspicious, he or she will usually tell the resident director (RD), who then goes to the police. The RA or RD will likely just issue a warning if they catch something illegal, but if they call the police, you could end up in a lot of trouble. Be smart, and if you want to really go nuts, go off campus.