Many ancient cultures and religions engaged in various techniques and used various substances to instigate religious experience and to alter perception. These techniques of psycho-sexual drug yoga reached an unparalleled level of sophistication that arose and was often cloaked in practical terms of alchemy and metallurgy. The Vedic tradition describes this plant-based ritualism as soma, which has been identified by Gordon Wasson as the mushroom Amanita muscaria. This article traces these soma-influenced sects of esoteric Buddhism that exerted influences from India, China and Tibet to Japan. Some of the key components, practices and symbolism are retained despite numerous cultural filters. Japan’s tradition of esoteric Buddhism can thus be seen to have preserved and incorporated the soma/amrita mushroom lore into its own traditions of mountain ascetic mystics. Keywords—Amanita muscaria, esoteric Buddhism/Tantra, Japanese ethnomycology, soma