I can swear I came across a study I found, I believe, on Erowid, which noted this link had a lower instance of increased mental illness than religious "meccas" do.

In light of that evidence, it's entirely possible the human experience itself, and not some more mechanistic action or first order effect of the drug, cause the increase in mental illness.

I'm trying to find this source, but am coming up short and on mobile, but will look into it later.