For the most part, you can make the drug scene what you want it to be. While many students drink alcohol, there are some that don't, and recreational drugs can be avoided or found fairly easily. Marijuana is definitely the most common drug, and some people do ecstasy or shrooms. Some students have encountered more hard-core drugs like crack, cocaine, or heroin, but those are much more rare-shooting up is definitely not a typical house-party activity. Beer bonging and doing body shots are a different story. The point is, the UW campus is so diverse that there are always students to be found who participate in drugs. If you are a drug user, then you shouldn't have too much trouble tracking down that crowd. And in turn, unless you have a roommate who hotboxes the room when you're asleep, you shouldn't have too much trouble avoiding it.
All big frat parties and virtually all house parties have some type of alcohol around. In fact, alcohol is pretty much a prerequisite of a party, whether it's BYOB (bring your own beer) or provided. Alcohol is definitely more prevalent in the Greek system. Many frats have alcohol-provided parties on a weekly basis. At parties at houses and frats, it varies how common it is to find people smoking a bowl. Some parties have a lot of stoners around, others only have alcohol and no recreational drugs. Again, it's pretty much within your power to find or avoid the drugs.