In 1978 R. Gordon Wasson, the chemist Albert Hofmann and the classicist Carl Ruck published a proposal that the Eleusinian kykeon was psychoactive, and that the agent was ergot, the fungus that grows on cereal grasses and from which Hofmann had first synthesised LSD. The case rests on several strands: the drink was made from barley, ergot infects barley and rye, the Mysteries produced an experience that participants described as overwhelming and transformative, and Eleusis was a grain sanctuary where the connection between the fungus and the crop would have been available to observe.
The objections are substantial and have not been met. Ergot as it grows carries alkaloids that are severely toxic, causing the convulsions and gangrene of the medieval outbreaks, and separating a psychoactive fraction from a poisonous one by any technique available in antiquity is the weak point of the argument. Critics also note that the hymn describes a specific recipe that does not mention any additional agent, that a mass initiation of many hundreds of people each year would require reliable dosing of an unreliable natural material, and that ancient descriptions of the experience are compatible with fasting, darkness, exhaustion, staging and expectation without any pharmacology at all.
Neither side can produce the evidence that would decide it, and both know which evidence that would be. No residue analysis of a vessel securely tied to the Eleusinian rite has settled the question, and the silence of the initiates guarantees that no text will.
The atlas records the proposal as debated: it has serious advocates and serious opponents, and no result has closed it.