Back in my teenage years I took pretty much every psychedelic I could access, and trip-sat (like babysitting) for about two dozen of my friends over the course of a few years. I found in tripsitting that psilocybin was among the more difficult to manage psychedelics, especially for first-timers. I found that 2C-B/E, DOC and LSD were the best-tolerated substances among people that weren't "psychonaut veterans."
This is purely anecdotal and in no way meant to imply that I know what the hell I'm talking about. I only bring it up as a thought that popped into my head relating to the use of psychedelic drugs in therapy.
Also, no. I do not know where to get any of this stuff anymore. Haven't known for over a decade.