Books like Cleansing the Doors of Perception: The Religious Significance of Entheogenic Plants and Chemicals

One would not expect Huston Smith to write about this subject, but he does and does it well and responsibly - I appreciate that he replaced 'psychedelic' by 'entheogenic'. Interesting chapters on 'soma' and LSD.Important statement: Although the mind-altering substances he talks about can induce religious experiences that are indistinguishable from spontaneous theophanies or those induced by other means (fasting, dancing, etc.), they may also completely lack any religious feature - this depends on the person, setting etc. Above all one should focus on a religious life rather than on religious experiences. Moreover, there is the 'tremendum' part of such experiences, the 'fear and awe' of Rudolf Otto's 'mysterium tremendum et fascinans'.