I have more friends mucked up by LSD like drugs than any other type - at any rate three of them and I don't have much in the way of junkie of alcoholic friends. I say LSD like as they all took other stuff. From my n=3 data I'd say if you do it more than once a week for more than two years you have a good chance of ending up like your friend.
It's called "getting fried". Know many people that fried themselves doing that stuff recreationally every weekend. Good rule of thumb is if they can't hold their alcohol they won't be able to hold their psychs.
