One thing I consistently saw in people that tried these substances is that abusing them -- heavy, careless use -- can be very harmful. I would not recommend it. I saw a few people in my youth who kind of just "never came back."

They seem able to produce beneficial effects in moderation and if treated with respect. I suppose that's true of lots of other powerful technologies. Treat them with respect and they can work well, but abuse them and they'll harm you.