Beakers excavated from sites in southeastern Illinois were apparently used by members of the Cahokia tribal group for beverages made with Ilex vomitoria and Ilex cassine, two forms of the holly plant that have substantial amounts of caffeine and theobromine, scientists said.
"For many groups, Black Drink played a central role in the ritual cleansing and purging of the body when combined with fasting and vomiting that was an essential precursor to conducting any important activities," authors of the research published in the Proceedings of the National Academy of Sciences wrote.
The ritual beverage was prepared by drying holly leaves and small twigs, then placing them in a large pot with water, boiling them, and agitating the liquid into froth.
Native Americans were drinking Black Drink long before contact with Europeans, the researchers said, and evidence points to use of the plants far north of their natural habitats, implying some trade activity.
Researchers from the University of New Mexico, the University of Illinois, Millsaps College and the Hershey Technical Center were involved in the study.
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