My daughter is 19, and has never been drunk or high. I didn't even raise her to be like that.. I hoped it's the choice she would make, but I didn't really expect it. She made the choice herself. She has no interest in drugs or alcohol, and I don't think she ever will. She has only two friends who party, and all the rest made the same choice she has made.
This is ds1, as well. He was in a play festival at college this past week, and in one of the plays (these were one act plays written by the writing students, and performed by the students in my son's acting program), he stood at the front of the stage and said, "you know what's awesome? Marijuana". I'm not sure if his friends, girlfriend and I had the harder time not cracking up. He's like the last person who would ever say that in real life, because he just has no interest in drinking, drugs, etc. While I'm glad he's going this route (he has three addict/alcoholic grandparents, and his dad is also an addict), I have no idea how it happened. I was raised in a much more clearcut "don't drink or do drugs" environment than he was - although not the really hardcore view that I've come across elsewhere - and my sister and I both smoked it regularly, my brother tried it, and we all swilled booze like sodapop.
And, yeah - ds1's friends are mostly the same. He has a couple who drink too much, and smoke some pot, but most of them are drug free and mostly alcohol free. (They're legal drinking age here, so there are some occasional "go to the pub and have a couple of beer" type nights. It's just not a focus for this group.)