For what it's worth, I went to my instructor when I was in culinary school some years ago, and pointed out a serious health infraction one of the students had engaged in..(dropped an entire pan of pate on the filthy meat fab floor, scraped it back into the pan, and baked it..to be served in the restaurant), and was rewarded with a one letter drop in my grade and told it was none of my business. (the pate got cooked and served..)I know this isn't drug use, but it was still a very serious problem. I never spoke out about anything else like that again.
Also, a few of the students who went to school with me also had obvious drug problems, but none of them made it through to finish..If you have an advisor, or an instructor you trust, perhaps you could open up to him or her. Good luck, and keep your distance from that person in class.