The brother of a friend I once had went insane from doing deliriants. That was quite the thing to watch over the years. Very disturbing. Over time he started taking cigarette butts out of the disposal bins you find outside of stores and smoking down what little of them remained. He ended up stealing his mother's car, crashing it, and was found by the police walking down the middle of the road mumbling incomprehensibly to himself. He wasn't on anything at the time as far as I'm aware, he was just genuinely far gone.
I was always more of an observer and never really did anything, but I did spend a fair bit of time on erowid learning about phenethylamines, tryptamines, and the rest out of interest. I also briefly knew some people who were getting ridiculously good deals on MDMA, but I was very skeptical of it. Again I never did anything myself so I can't say anything as far as the effects of what they got, but they were getting it in big crystalline chunks, and having heard plenty about how supposedly often people get scammed over MDMA, I did always wonder what it actually was that they got their hands on. It could have been MDPV/bathsalts for all I know, but I'm not an expert obviously.
I still want to read Hoffman's book, "LSD, My Problem Child", though, since I figure he probably has an interesting take on it all, and obviously knew much more about it chemically than I do.
Observing people like that was interesting, but I'm glad I'm far away from anyone like that now, to be honest. The only thing lost on my part is being able to listen to Spacemen 3 without being reminded of some rather dark images. Really great band though.
EDIT: The "ego death" thing always got a kick out of me, I forgot to say. Everyone became a genius and prophet because they had a colorful fever dream while awake.