I don't want to disagree with your opinion of the cause of your friend's psychosis, as you observed the process and I didn't, but as a general statement I'd like to put out there that the time of life when schizophrenia presents (late teens, twenties, early thirties) correlates with the years when people usually experiment with drugs. This has been true since before LSD existed.

http://schizophrenia.com/photos/szage.onset.gif

from

http://www.ncbi.nlm.nih.gov/pubmed/8178665?dopt=Abstract