Like DMT and ayuhausca? I don't have any personal experience, but from what I've heard, they can initiate mystical experiences that can be very transformative for the person. It creates similar effects to what you hear from some advanced spiritual people -- loss of ego, expansion of consciousness, a feeling of merging with everything, greater perspective and wisdom.
I'm not personally sold on it, though. For one, it's a powerful drug, so anything that happens under its influence ... how do you trust that, when you get back to non-drugged awareness? And how do you bring that experience back to normal awareness, since memory is state-dependent (meaning, your memory of the experience is dependent on being in that drugged state)?
And then there's the issue of integration. How well is that sort of experience integrated? The person has a pre-set level of maturity and understanding. It's not like the drug permanently transforms them. It just gives them an additional experience layered on top of all their old stuff. How does that fit? Is the individual able to take the experience and make use of it, or is it so alien to the person's basic adjustment that any gains are basically lost within a few months?
I'm also suspicious of spiritual shortcuts. Easy path to enlightenment? Yeah, I don't know. I think it's better to work through normal channels, rather than take shortcuts.
I'm also suspicious of "special effects" spirituality, by which I mean a type of spirituality that emphasizes dramatic breakthroughs, peak experiences, big "Wows." It gets the headlines, which in itself makes me suspicious. I have more trust in let's say ordinary, commonplace spirituality. You know, introspecting, trying to grow as a person, learn more, open up, see behind the veil as best you can, work on your character, try to gain in wisdom. None of that is flashy or exciting, and it comes slowly, bit by bit, not in some big rush. But it's the tried and true method, rather than something new and flashy, and I trust it more.
So, I wouldn't pursue the drugs myself. Still, some people do report big changes from it, and I'm no expert in it.