I didn't find the exact book I was looking for ... however this piece makes for a pretty good start on the psychedelia/religion subject.
Psychedelia Past, Present and Future
A censored and taboo aspect of human culture that has always existed from since time immemorial to the present day and which may be a forbidden doorway to divine realities.
This section deals with what is certainly one of the most controversial topics in the broad and diverse world of spirituality, religion and mysticism. It concerns the idea that certain plant extracts, fungaloid or cacti preparations and also specific chemical formulations; can induce various and varying states of connection with that which one may or may not want to call God. At the outset, I'll say here that in no way do I wish to recommend, condone or promote the use of these powerful and sometimes harmful substances. It is necessary however to explore the role and nature of psychedelic substances; if we are to fully understand the early history of world religion and also some aspects of the spiritual landscape today.
When we explore the early history of religion and examine the various holy scriptures of different faiths, then we find mentioned mysterious substances with divine connotations, which were either eaten or drunk. So in the Bible we have the enigmatic manna or the food that fell from heaven. In the Bhagavad Gita and the Rig Veda we find described the Soma drink, which allowed people to enter into the divine. And in early Zoroastrianism we find mention of the mysterious Huoma, used by the Magi for their sacred rituals. When we examine the mystery traditions of ancient Greece we discover the Kykeon, the beverage that played a central role in the Eleusian mysteries. And the Greek Oracles of Delphi and the Roman Sybil of Cumae are believed to have achieved their prophetic states of mind through the inhalation of mind altering volcanic hydrocarbon gases emanating from the depths of the earth. Going over to ancient Egypt we correspondingly find the use of the plant, the Blue Lotus of the Nile, by the Egyptian high priests. This Blue Lotus plant may be related to the lotus of the 'Lotus eaters' in the classical Greek myth Odysseus. When mythology is understood as spiritual allegory then this would make perfect sense. If the journey of the mythological hero is a journey of spiritual development and discovery then a visit to the land of the lotus eaters can be understood as a reference to some psychedelic substance. Also it is worth mentioning here that 'Soma' which was mentioned earlier, means 'to press out and extract' in Sanskrit. And there exist ancient Sanskrit texts that describe the Lotus plant as soma. So it is reasonable to deduce that in antiquity, something was pressed out and extracted from lotus plants, which was then prepared as a beverage and ingested. It is very possible that the Lotus eaters and the Soma drinkers were actually partaking of the same psychoactive ingredient. Moving on to the ancient civilization of Babylon we find the myth of Gilgamesh, which is the oldest recorded story known to man. In the tale, the hero Gilgamesh is told to seek out the plant of immortality, another obvious reference to a psychedelic plant.
When we examine all these facts together then a clear picture emerges. It is one where we can see that early religion or proto-religion involved the use of psychedelic substances in order to facilitate communion with the divine. This view is further supported by the use of psychedelic substances in many primitive indigenous religions practiced by native tribes in the world today. Also many scholars believe that Taoism, which is the native spiritual tradition of China, was derived from Siberian Shamanism. Almost without exception, shamanistic practice goes hand in hand with the use of these facilitator substances i.e. psychedelics. So at the dawn of civilization, our primitive ancestors discovered a door into the divine, that seems almost purposefully set up by the Cosmic Intelligence, in order that we may enter it. That is certain plants and fungi acted as gateways to the transcendent. The visions and mystical insights obtained through using these substances certainly found their way into the primitive systems of religious thinking that would later evolve to become the great faith traditions of the World.
I have a bit more to share regarding the evolution of religion from it's very early Animistic and Shamanistic beginnings ... but I'm not sure if I have the energy for it right now ... to be continued!