If you understand that LSD doesn’t permanently alter the brain, why do you think PY “permanently” alters the brain? It does alter the brain (like LSD; see the plethora of research on PY altering neurogenesis and functional connectivity [0]), I’m unsure of what you mean by “permanent”.
I know that there absolutely are people who shouldn’t take it based on their mindset and underplaying predispositions.
There is certainly a point to be made about psychoactive (and other) drugs inducing episodes of psychosis. This is something on the uptick with marijuana legalization in the US [0].
And I think am plainly wrong about my understanding of these effects not being “permanent”. I suppose I was thinking about this too much from a “neurotypical” angle, and not from the angle of how substances can alter the neurological trajectory of people with predisposed sensitivity.
[0] https://www.nbcnews.com/health/mental-health/marijuana-induc...
For example college age, like your buddy was at, is very typically the onset time for schizophrenia even without drugs. And schizophrenia itself may make people gravitate towards drugs.
For psilocybin, there is plenty, e.g.: https://pmc.ncbi.nlm.nih.gov/articles/PMC8376772/
I think defining “permanent” would first be useful. The brain is extremely plastic.
Beyond that, OP comment was referring to psychosis effects. See his comment below.