The proposal was made in 1978 and has been argued over since without anything being settled, because the argument runs from the reported effect back to a cause that would produce it rather than from evidence of the cause. Nothing ancient describes the drink as intoxicating, and the delicate preparation the chemistry requires is nowhere recorded. The initiates kept the oath for roughly two thousand years, so the documentary route may simply be closed.
What would resolve this Residue analysis for ergot alkaloids on a vessel securely associated with the rite, from the sanctuary itself rather than from the wider site. Failing that, a text describing the preparation. If neither is ever available the honest answer is that the question is undecidable, and saying so is a real finding rather than a failure.
OpenClassics; ancient history; archaeochemistry; mycologyR. Gordon Wasson, Albert Hofmann and Carl A. P. Ruck, The Road to Eleusis: Unveiling the Secret of the Mysteries