So, it’s the bit about drugs that caught your eye, is it? Far be it from me to judge!
The whole thing is unclear, but what we do know is that there are many laments to the death or loss of Soma found in the Vedic literature. In my article on mythology I argued that the death of God is the prime mythic theme, and this is one instance of it.
Generally speaking, part of this theme revolves around the distancing from direct spiritual experience, as the wild nature-religions, with their blood sacrifices and orgiastic visions, are gradually tamed and civilized; God is imprisoned in Churches, and his fierce will is subject to the learned opinions of the theologians.
It is thought that the soma, whatever it referred to, was a psychotropic substance that the Aryans had access to in the homeland (= ambrosia in Europe), which was no longer found in India.
But the physical availability is just one part of it; at the same time, as the spiritual movement evolved there were two quite contradictory forces: towards domesticity, doctrine, consistency, an imposition of orthodoxy in pursuit of social dominance; and a need to evolve the incoherent visions of the drug/rituals towards something deeper. The first of these forces led to the caste system and the Brahmanic orthodoxy who the Buddha butts heads with throughout the suttas. The second led to the Upanishads and the spirit of questing we also see in the Suttas, where Brahmins from Brahmayu to the students of the Parayanavagga seek out the Buddha’s advice.
But I do think we are safe to say that in ancient India, as in modern western culture, the emergence of meditation was influenced by drug culture. The transformation of drugs opens up the possibility of altered states of consciousness, and teaches us just how deeply our experience of reality is constructed by our assumptions. At the same time, since the experience is ultimately chaotic, it quickly reaches it limits. Assuming you don’t kill too many brain cells, it’s natural to see whether there’s a safer and more powerful way of transcending the limits of consciousness.