Long before Ethiopian monks in the 9th century discovered that coffee tree fruit helped them stay awake during evening prayer (according to legend, anyway), communities in Southeast Asia have been chewing betel nuts—the seeds of the areca palm and a stimulant that heightens people’s alertness, energy, euphoria, and relaxation—since antiquity. But new research indicates that betel nut chewing has been practiced for even longer.

By studying ancient dental plaque from Bronze Age individuals in Thailand, an international team of researchers suggests that people were consuming the stimulant 4,000 years ago. This novel approach paves the way for future investigations of ancient behaviors in the absence of traditional archaeological evidence.

“We identified plant derivatives in dental calculus from a 4,000-year-old burial at Nong Ratchawat, Thailand,” Piyawit Moonkham, an anthropological archaeologist at Chiang Mai University and first author of the study published yesterday in Frontiers in Environmental Archaeology, said in a statement. Dental calculus, also called tartar, is hardened dental plaque. “This is the earliest direct biomolecular evidence of betel nut use in south-east Asia.”

Moonkham and colleagues analyzed 36 dental calculus samples from six individuals from Nong Ratchawat, a Bronze Age archaeological site in central Thailand. The team also produced their own betel liquid samples to investigate the interactions between ingredients and make sure their analysis could accurately detect the psychoactive compounds.

“We used dried betel nut, pink limestone paste, Piper betel leaves, and sometimes Senegalia catechu bark and tobacco. We ground the ingredients with human saliva to replicate authentic chewing conditions,” Moonkham explained. “Sourcing materials and experimentally ‘chewing’ betel nuts to create authentic quid samples was both a fun and interesting process.” A betel quid is a chewing mixture consisting of the areca nut and other ingredients, such as those listed above. It’s worth mentioning that a heavy use of betel nuts can eventually lead to health risks such as oral cancers and heart disease.

The team’s analysis revealed traces of arecoline and arecaidine in three of the samples, all from the same individual—organic compounds present in betel nuts as well as coffee, tea, and tobacco, which can have a significant impact on a person’s physiology. In other words, betel chewing has likely existed for at least 4,000 years.

“In essence, we’ve developed a way to make the invisible visible—revealing behaviors and practices that have been lost to time for 4,000 years,” said Shannon Tushingham, senior author of the study and associate curator of anthropology at the California Academy of Sciences. Furthermore, “the presence of betel nut compounds in dental calculus does suggest repeated consumption, as these residues become incorporated into mineralized plaque deposits over time through regular exposure.”

While consistent betel juice chewing usually stains teeth, the researchers did not identify any such staining. They suggest that this could be due to different consumption methods, ancient teeth cleaning practices, or processes that prevented the stains from lasting over 4,000 years. They also didn’t find any evidence indicating that the individual’s burial was special compared to the others—evidence that, presumably, might have provided insight into why the individual consumed betel nuts.

“Psychoactive, medicinal, and ceremonial plants are often dismissed as drugs, but they represent millennia of cultural knowledge, spiritual practice, and community identity,” Moonkham concluded. “Archaeological evidence can inform contemporary discussions by honoring the deep cultural heritage behind these practices.”