Initiates of the Eleusinian Mysteries participated in the most famous secret religious rites of ancient Greece by drinking a barley beverage called kykeon that was likely contaminated with psychoactive ergot.

The drink at the center of Eleusis

At Eleusis, a sanctuary northwest of Athens, initiation unfolded as a tightly guarded ritual rather than a public ceremony. Its central drink, kykeon, was a simple barley-based beverage. The initiate’s experience depended on more than its ingredients: fasting, the journey to the sanctuary, ritual actions, and a night spent in a dark hall all shaped the setting in which the drink was consumed.

That setting helps explain why kykeon has attracted so much speculation. If the barley had been infected by ergot—a fungus that grows on grain—it might have carried alkaloids, naturally occurring chemicals capable of affecting the nervous system. Some scholars have proposed that a preparation of ergot could have contributed to the initiates’ experience.

A plausible mechanism, not a settled answer

Ergot is not a single, predictable drug. Its chemical effects vary, and the presence of the fungus alone would not establish that a drink contained an active or safe dose. Preparing grain and brewing a beverage could also change what compounds remained. The surviving evidence does not establish that Eleusinian kykeon was psychoactive, much less reveal exactly how it was made.

The proposal nevertheless offers a concrete possibility: a familiar grain drink may have served as the ritual’s hinge, linking ordinary bodily sensations—thirst, hunger, drinking—to an extraordinary, carefully staged night. Because initiates were forbidden to reveal what they saw or experienced, the precise role of the drink remains unknown. The enduring mystery is not simply what was in the cup, but how its contents worked together with the ceremony around it.