The drug scene at Santa Clara is pretty tame, centering mostly around alcohol and marijuana. While both are commonly used among students, alcohol tends to be most students' drug of choice. While many students drink, not all do, and campus organizations are pretty good about offering alternative activities for those who don't. Students who choose not to drink usually aren't pressured to do so, but some may feel left out at big off-campus parties where almost everyone else is engaged in some drinking-related activity.
Campus Safety strictly enforces campus alcohol and drug policies. Depending on the violation, students caught drinking underage or using drugs can get stuck with a fine between $50 and $100, community service, and a letter sent home. But students usually only get caught if they're visibly intoxicated or making a lot of noise in their rooms, so avoiding trouble just requires using common sense.