Soma (Sanskrit: सोम), or Haoma (Avestan), from Proto-Indo-Iranian sauma-, was a ritual drink of importance among the early Indo-Iranians, and the later Vedic and greater Persian cultures. It is frequently mentioned in the Rigveda, which contains many hymns praising its energizing qualities. The world’s oldest spiritual text and the scriptural foundation of Hinduism, mentions the sacramental substance ‘soma’ frequently, describing it both as a god and as an intoxicating liquor made from juice obtained from the crushing of a plant. To the Brahmin priests who drank it, it was said to have given strength, magnitude and brilliance; indeed it is suggested in the Vedas that by ingesting soma you became Soma (the god) and thus gained immortality.

It is apparent that soma was the focal point of Vedic religion. The Rig Veda contains 1028 hymns of which 120 are dedicated to Soma, 114 of these comprising the 9^th Mandala or the Soma Mandala which is dedicated solely to Soma Pavamana or ‘purifed Soma’. Additionally, whilst other religions have related their sacraments to representing their deities, for example the Christian Eucharist represents the blood and flesh of Christ and the Mexican Indians refer to the mushroom ‘peyotl’ as ‘teonanacatl’ or ‘god’s flesh’, soma appears to be the only plant or substance that man has ever actually deified

Although much is written about its use, the identity of the plant from which soma was made appears to have been lost around 1000 B.C.E. This was around the time that the Aryans (who recorded the Rig Veda) migrated from the mountainous regions of Afghanistan, now known as the Hindu Kush, to the fertile flatlands of modern day north-west India. It is thought by many that the identity of the plant was either suppressed to prevent its use by the lower classes and subsequently forgotten, or that the plant only grew in the mountainous regions and not on the plains below.

R. Gordon Wasson, who is also credited with rediscovering ‘teonanacatl’ the sacred mushroom of Mexico, became synonymous with the search to identify the plant from which Soma was derived. He looked at a number of psycho-active plants including the mint Lagochilius inebrians, Convolvulacea or Morning Glory seeds, the fungal parasite Claviceps purpurea or ergot (from which LSD is derived), and the mushroom Psilocybe (Stropharia) cubensis before deciding that he thought the best candidate was Amanita Muscaria (the Fly Agaric mushroom). Wasson’s evidence came mainly from an analysis of soma's physical attributes, described in the Vedas, which he believed correspond to morphological characteristics of A. muscaria. For example, citing several Vedic references to soma as the "mainstay of the sky" and the "foundation of the earth," Wasson observed that "the sturdy stanchion with its resplendent [white-flecked, brilliant red] capital that is the fly-agaric lends itself well to this poetic conceit." He specifically dismissed "a creeper, a climber, any vine, some species of Sarcostemma or Ephedra" as viable alternatives because, in his opinion, no poet would use the same language to represent these plants.

Further, the Rig Veda describes Soma as being a plant extract, yet nowhere does it mention blossoms, fruits, seeds, leaves, branches, bark or roots, referring instead to stems and caps, suggesting to Wasson that Soma was derived from a mushroom. His belief that Amanita muscaria was the specific mushroom is drawn from further information regarding the exclusively mountainous locations in which it is recorded as growing and the colours described in the Rig Veda, that correspond better with A. muscari than with any other mushroom.

Developing his argument supporting Amanita Muscaria he suggests that evidence in the Rig Veda prevents the psilocybin containing mushroom Stropharia cubensis (also known as Psilocybe cubensis) from being Soma, as it grows in the dung of cattle and not in the mountains, but that there is evidence that Stropharia cubensis (referred to in Sanskrit texts as pūtika) was the substitute used. Additional evidence is provided from other sources. In the Santal language of North East India, there are no genders, and nouns are either animate or inanimate, things are either with or without a soul. The whole of the animal kingdom is animate, but the vegetable kingdom is inanimate with the single exception of one species of mushroom, identified as Stropharia cubensis, and referred to in Santal as pūtka. There is a belief amongst the Santal that pūtka grow where lightning has struck the ground, possibly because the spores of mushrooms are invisible to the naked eye, and hence they appear to have been spawned without seed. There are obvious parallels here with soma, because in the Rig Veda the Vedic Brahmans believed that soma was procreated by the Parjanya, the god of lightning. Wasson also questions whether the fact that S. cubensis grows in the dung of cattle is the reason why cows are sacred in Hindu culture.

Conversley, Terrence McKenna's experience of both Stropharia Cubensis and the Fly Agaric suggested to him that Soma was in fact Stropharia Cubensis, due the variability of the effects of the Fly Agaric and that personal experience suggested that Stropharia Cubensis produced ecstasies closer to those described in the Rig Veda than did the fly Agaric.

Other writers, such as Andy Letcher, believe that Soma was not psychoactive at all. They suggest that R. Gordon Wasson's writings came at a time when recreational psychedelic drug use was being met with a legislative response (1968) and that a long history of entheogenic drug use gave validity to contemporary use.