4,000-year-old dental plaque uncovers evidence of people eating psychoactive betel nuts

Archaeological graves with artefacts found at Nong Ratchawat. (Image: Piyawit Moonkham)

By digging into the smallest corners of history, scientists have now found clues hidden not in bones or tools, but in ancient plaque. The surprising discovery offers fresh insight into how people lived, what they valued, and what they consumed thousands of years ago.

Evidence of betel nut chewing in Bronze Age Thailand

Researchers from Chiang Mai University and the California Academy of Sciences have identified chemical traces of betel nut chewing in a 4,000-year-old burial. The find was made at Nong Ratchawat, an archaeological site in central Thailand where 156 human remains have been excavated since 2003.

The evidence came from hardened plaque on ancient teeth, known as dental calculus. Scientists analysed 36 plaque samples from six individuals buried at the site. In one case, plaque from a molar held the chemical compounds arecoline and arecaidine. These are found in betel nuts and known to affect mood and energy.

Dr. Piyawit Moonkham, lead author of the study, said this is the earliest direct biomolecular evidence of betel nut use in Southeast Asia. Dr. Shannon Tushingham, the study’s senior author, added that the method gives access to ancient practices that leave no visible trace.

How researchers confirmed the ancient practice

To support the findings, the team recreated a traditional betel quid using dried betel nuts, Piper leaves, limestone paste, bark, and saliva. They used this mixture to test how betel ingredients behave under analysis. This process helped confirm that the compounds in the tooth came from betel consumption.

The absence of red or brown stains on the teeth was also noted. Researchers believe this could be due to oral hygiene, alternative chewing styles, or natural wear over time. The lack of stains does not mean the practice was absent.

A new method may rewrite parts of cultural history

Burial 11, where the betel traces were found, did not show signs of elite status. Some beads were present, but no strong evidence linked the individual to special treatment. However, scientists believe more research may reveal how widespread betel use was in early Thai societies.

Dental plaque is now seen as a valuable source of lost cultural practices. The method used in this study could be applied to other burials in the region. It may uncover the presence of psychoactive plant use in places where no other clues remain.

“Understanding traditional plant use gives us a richer view of history,” said Dr. Moonkham. “These practices are not just habits but are tied to identity, medicine, and belief.”

The research was published in Frontiers in Environmental Archaeology.