Some scholars believe that the power of the Eleusinian Mysteries came from the kykeon‘s functioning as a psychedelic agent. Barley may be parasitized by the fungus ergot, which contains the psychoactive alkaloids lysergic acid amide (LSA), a precursor to LSD and ergonovine. It is possible that a psychoactive potion was created using known methods of the day. The initiates, sensitized by their fast and prepared by preceding ceremonies, may have been propelled by the effects of a powerful psychoactive potion into revelatory mind states with profound spiritual and intellectual ramifications.
While modern scholars have presented evidence supporting their view that a potion was drunk as part of the ceremony, the exact composition of that agent remains controversial. Modern preparations of kykeon using ergot-parasitized barley have yielded inconclusive results. Terence McKenna argued that the mysteries were focused around various entheogenic plants, but at present no consensus has been reached. The size of the event may rule out Amanita or Psilocybe mushrooms as active ingredient, since it is unlikely that there would have been enough wild mushrooms for all participants.
Another theory is that the kykeon was an Ayahuasca analog with a shrub that also functions as a Monoamine oxidase inhibitor. The most likely candidate for the DMT containing plant, of which there are many in nature, would be a species of Acacia. Other scholars however, noting the lack of any solid evidence and stressing the collective rather than individual character of initiation into the Mysteries, regard entheogenic theories with pointed skepticism.