If you find this topic interesting I'd recommend "Writing on Drugs" by Sadie Plant which is basically about the modern-European-centric cultural history of drugs and philosophy (feature Coleridge, Freud, etc.)
Fundamentally, I'd say psychedelics explicitly reveal that our sensory-informated reality is really just a somewhat fickle map of reality. This is particularly seen in the visual field, where images from memory can get fed back into normal sensory processing. One of the more accurate pop-culture references to what this is like was seen in this image from the first "Matrix" movie:
Under higher doses one can completely lose grasp of visual perception (a rather dangerous state to be in if one is around say, high cliffs etc., which accounts for all the cautionary advice about safe settings and so on) but in this sort of intermediate state one can still navigate using one's sensory-supplied map of reality, but it really is just a map, and we are really in a similar position to that of a blind person using echolocation to find their way around. That's the 'great insight' of psychedelics IMO (which also makes psychedelics an incredible aid for 3D visualization in the arts and sciences, I think).
They can, however, also be emotionally and psychologically disturbing (fear, panic, paranoia, etc. are not unheard of responses).
https://www.goodreads.com/en/book/show/580859
For a broader overview of the global history of psychedelics, "Plants of the Gods" by Schultes, Hofmann, and Ratsch:
https://www.amazon.com/Plants-Gods-Sacred-Healing-Hallucinog...
Fundamentally, I'd say psychedelics explicitly reveal that our sensory-informated reality is really just a somewhat fickle map of reality. This is particularly seen in the visual field, where images from memory can get fed back into normal sensory processing. One of the more accurate pop-culture references to what this is like was seen in this image from the first "Matrix" movie:
https://i.stack.imgur.com/zymAc.gif
Under higher doses one can completely lose grasp of visual perception (a rather dangerous state to be in if one is around say, high cliffs etc., which accounts for all the cautionary advice about safe settings and so on) but in this sort of intermediate state one can still navigate using one's sensory-supplied map of reality, but it really is just a map, and we are really in a similar position to that of a blind person using echolocation to find their way around. That's the 'great insight' of psychedelics IMO (which also makes psychedelics an incredible aid for 3D visualization in the arts and sciences, I think).
They can, however, also be emotionally and psychologically disturbing (fear, panic, paranoia, etc. are not unheard of responses).