The question that scientists and other empiricists ask when considering ideas is not "is it true?" but "is it useful?"
Do people bring back useful (in the engineering sense) knowledge from their times tripping/rolling? Are they more likely to experience e.g., fruitful insights akin to Kekulé's vision of the benzene ring as an ouroboros, as a result of having consumed these drugs? If so, then the drugs may indeed live up to the claims that they grant access to "truer and deeper" levels of reality. Otherwise, their users are simply fooling themselves. (Although fooling yourself can prove useful; the almost universal belief in deities among humans fulfills some sort of purpose, though it is my belief that that purpose is no longer relevant.)
You're using the word 'useful' as a euphemism for 'practical,' and missing the point. You cannot expect to fully grasp a wholly subjective experience through a predominantly rational mindset. Better to simply discard the intellectual point of view for this topic and attempt to engage it otherwise.
Do people bring back useful (in the engineering sense) knowledge from their times tripping/rolling? Are they more likely to experience e.g., fruitful insights akin to Kekulé's vision of the benzene ring as an ouroboros, as a result of having consumed these drugs? If so, then the drugs may indeed live up to the claims that they grant access to "truer and deeper" levels of reality. Otherwise, their users are simply fooling themselves. (Although fooling yourself can prove useful; the almost universal belief in deities among humans fulfills some sort of purpose, though it is my belief that that purpose is no longer relevant.)