Long ago, at a pre-Columbian ritual center across the Mississippi River from present-day St. Louis, the home of Budweiser, people were heartily imbibing a caffeinated tealike beverage commonly known as “black drink.” The chemical residues found in their porous, unglazed ceramic mugs tell the tale.

Early European explorers described the drinking practice throughout what is now the southeastern United States. Indian men consumed large portions of black drink brewed from toasted holly leaves and bark and boiled it in water. Then they would go off to vomit. Whether this was the effect of the drink or was self-induced is not clear; anyway, the practice was a ritual purification in preparation for important community undertakings like religious ceremonies, political councils or ballgames and war.

For the first time, researchers have now found direct evidence that the use of black drink goes back as early as A.D. 1050 at what is now Cahokia, Ill., which was the largest known pre-Columbian site north of Mexico. The chemical analysis identified the primary ingredients of the Cahokia brew: caffeine, theobromine and ursolic acid.

“Ursolic acide is the biomarker that tells us, yes, this was made from holly,” Patricia L. Crown, an anthropologist at the University of New Mexico, said in an interview. She was the lead author of a report published Monday in the journal Proceedings of the National Academy of Sciences.