Indo-European Use of Entheogens
Kalin
It has been widely speculated that psychedelics were used in certain rituals in almost every branch of European polytheism. It has also been assumed that many peoples kept this practice secret, or rather sacred, and guarded it from people who would abuse it. This is the possible origin for some esoteric orders in which the iniated were shown "secrets" that pertained to spiritual developement. This could be seen most plainly with the Eleusinian Mysteries, which very well could have used psychedelic substances like the Vedic "Soma" and Iranic "Haoma" may have.
The Vedic Soma
Soma is a thing of mystery for many, some think it was not even a tangible substance at all, but most in academics agree that it was a substance. Soma is also a lunar God who is also known as Chandra and is of course heavily associated with the use of the drink Soma. No one knows exactly what substance Soma was but there are a few likely candidates and some even think it was a mixture of several substances. Soma shares the same meaning and Proto-Indo-European root as Haoma, the Iranic equivalent. The theorized ingredients of Soma are Sarcostemma acidum, Ephedra sinica, Psilocybe cubensis, Peganum harmala and Amanita muscaria.
Ephedra is a common plant in Europe, Northern China, North America and even parts of Northeastern Africa and the Arabic Peninsula. In the United States, both Native Americans and Mormon Pioneers used Ephedra for its medicinal purposes as well as its caffeine-like effect. The early Indo-Aryan peoples used it for this purpose as well, which makes it a very likely candidate or ingredient for Soma.
Psilocybe cubensis, which grows in cow dung, is also common in North America and India and is a potent psychedelic mushroom, which very well could have been used as a vehicle for the spiritual experiences described in the Rigveda.
"We have drunk the soma; we have become immortal; we have gone to the light; we have found the gods. What can hostility do to us now, and what the malice of a mortal, o immortal one?" - Rigveda (8.43.3)
The Iranic Haoma
Little, really, is known about the Pre-Zoroastrian Iranic religion and all sources on it were written during the Zoroastrian era. As mentioned above, Haoma shares the same root as Soma and is identical in the old Iranian religion. In Zoroastrianism, which has roots in the original Iranian religion, they practice Yasna. Yasna is similar to the Vedic Yajna. It is a ritual which the ancient Iranians practiced as well as the Zoroastrians. The Zoroastrians would read passages and praise certain "angels." Haoma being like Vedic Soma, is also a deity. It should be noted that these rituals were conducted by the priests of the respective cultures. Haoma was also very important in the myth of the birth of Zoroaster himself.
The Scythians, who were nomadic relatives of the Iranians, also spoke a Iranic language and practiced their version of Iranic religion. They are assumed to have used Haoma as well. Other substances like hashish and opium were found, most likely as treatment for their wounded. Archeologists have even found 2,400 year old solid gold Scythian artifacts used to smoke hashish and opium.
The Mead of Poetry
Following the Æsir-Vanir War, to solidify their truce the Gods spat into a vat and made a man named Kvasir. Kvasir wanted to spread his immense knowledge to mankind but was killed by the dwarves Fjalar and Galar. His blood was poured into two vats and a pot and mixed with honey, making a mead that made anyone who drank it a poet and a scholar. An aspect of Soma that might be overlooked is the poetic one: like the Mead of Poetry, it was associated with poets and scholars. It hasn't really been theorized that the Mead of Poetry could have been a psychedelic or mind-altering substance, but it was certainly possible given the availability of psychedelic mushrooms in the regions in which Germanic peoples resided. Considering Vedic and Iranic cultures share a common ancestor with Germanic culture, it's not a far stretch to say the Mead of Poetry was, at least in the poetic aspect, the Germanic Soma.
The Eleusinian Mysteries
The Eleusinian mysteries were iniations into a cult of Demeter and Persephone which has its basis in an older agrarian cult. Their rites were closely guarded by iniates who were iniated every year at the Panhellenic Sanctuary in Eleusis. Despite this secrecy it was one of the most famous rites of the ancient Greeks. Various aspects were depicted on pottery, tablets like the one above, and in plays, some of which are still around today. There is reason to believe that these rites involved psychedelics, such as the various visions and revelations of the afterlife one would recieve after being iniated, and the consistency of these visions. The Eleusinian Kykeon, a drink of various ingredients, may have contained Ergot. Ergot is a fungus which can contain psychedelic alkaloids similar to LSD, and this may have been compounded with other substances in the Kykeon. In fact, Ergot was found in an Eleusinian temple dedicated to Demeter and Persephone. Not to say these revelations were any less significant. These rites were most likely practiced by early Christians and other esoteric sects, much like Zoroastrian Magi who still practice Yasna.
Conclusion
I may have used the term "entheogen" too loosely in this post but I hope the main point is not lost: our ancestors used these substances in a ritual context and were integral to their beliefs. Not meaning these beliefs were "made up" or simply a result of a drug induced psychosis, but used to better percieve the Gods and reality.
Thank you for reading.
To learn more about Soma and the Lunar Cycle:
https://taliesinsmap.blogspot.com/2020/09/the-great-lunar-cycle-horse-twins-and.html?m=1