The Kykeon reference article from the English Wikipedia on 24-Apr-2004
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Kykeon

Kykeon was a drink used in the Eleusinian mysteries to break a sacred fast. It was a mix of barley and pennyroyal.

It has been posited that one element of the kykeon was ergot and the hallucinogenic properties of that fungus helped provide the intense experience of the participants at Eleusis.