Humans have used psychoactive plants for their narcotic effects for thousands of years. Across Thailand, remains of areca nuts, plants used for their stimulant effects, have been found at burial sites.
To learn more about this practice, an international team of researchers examined 4,000-year-old teeth and found traces of compounds originating from areca nuts. This indicates that chewing these nuts has been practiced for thousands of years, if not longer, in the country. The study is the first to detect archaeologically invisible traces in dental plaque, revealing ancient behaviors and practices that otherwise might have been lost to time.
In Southeast Asia, areca nut chewing has been practiced since antiquity. The plants contain compounds that increase alertness, energy, euphoria and the consumer’s relaxation. Although the practice is becoming less common in modern times, it is deeply rooted in social and cultural traditions for thousands of years. Chewing areca nuts normally results in teeth stained dark brown-red to black.
However, non-stained teeth may not mean that people did not chew areca nuts. Now, using a new method, an international team of researchers examined Bronze Age dental plaque in Thailand and found evidence of areca nut chewing.
“We identified plant derivatives in the dental calculus of a 4,000-year-old tomb at Nong Ratchawat, in Thailand,” says the study’s lead author in Frontiers in Environmental Archaeology, Dr. Piyawit Moonkham, an anthropological archaeologist at Chiang Mai University in Thailand. “This is the oldest biomolecular direct evidence of areca nut use in Southeast Asia,” he adds.
“We demonstrated that dental calculus can preserve chemical signatures of psychoactive plant use for millennia, even when conventional archaeological evidence is completely absent,” notes Shannon Tushingham, senior author and associate curator of anthropology at the California Academy of Sciences. “In essence, we have developed a way to make the invisible visible, revealing behaviors and practices that were lost in time 4,000 years ago,” she reveals.
Hidden in dental plaque
In Nong Ratchawat, a Bronze Age archaeological site in central Thailand, 156 human burials have been excavated since 2003. For the present study, the team collected 36 dental calculus samples from six individuals.
Back in the laboratory, they removed small quantities of plaque from the samples and the chemical residues found in them were subjected to analysis. The team also used areca juice samples produced by themselves to ensure that psychoactive compounds could be reliably detected through their analysis and to understand the complex biochemical interactions between the ingredients.
“We used dried areca nut, pink lime paste, and, at times, Acacia catechu bark and tobacco. We ground the ingredients with human saliva to replicate authentic chewing conditions,” Moonkham says. “Obtaining the materials and ‘chewing’ areca nuts experimentally to create authentic samples was a fun and interesting process.”
The results showed that three of the archaeological samples — all from a single individual’s molar, Burial 11 — contained traces of arecoline and arecaidine. These organic compounds, found in areca nuts but also in plants such as coffee, tea and tobacco, have pronounced physiological effects in humans. This suggests that areca nuts were chewed 4,000 years ago in Thailand.
Proof of the “archaeologically invisible”
“The presence of areca nut compounds in dental calculus suggests repeated consumption, as these residues become incorporated into mineralized plaque deposits over time through regular exposure,” explains Tushingham. Thus, the absence of staining on teeth raises questions. It can be the result of different consumption methods, the team pointed out. It can also be due to dental cleaning practices after consumption or post-mortem processes that affected the preservation of stains over 4,000 years.
Although traces of areca nut chewing were found in samples from only one individual, there is currently no evidence that Burial 11 received special treatment or had elevated social status or a unique ritual significance compared with the other graves at Nong Ratchawat.
The presence of stone beads as funerary objects, however, may provide clues about the individual’s identity or life experiences. Studying more individuals at Nong Ratchawat and other sites to determine when and to whom these funerary objects were given could provide valuable evidence, the team said.
The methods applied by the investigators can be used to examine the remaining tombs at Nong Ratchawat and at other sites, they stated. “Dental calculus analysis can reveal behaviors that leave no traditional archaeological traces, potentially revolutionizing our understanding of ancient lifeways and the relationships between humans and plants,” says Tushingham. “This could open new windows into the deep history of human cultural practices,” she adds.
“Understanding the cultural context of traditional plant use is a broader topic that we want to expand — psychoactive, medicinal and ceremonial plants are often dismissed as drugs, but they represent millennia of cultural knowledge, spiritual practice and community identity,” Moonkham concludes. “Archaeological evidence can inform contemporary discussions, honoring the deep cultural heritage behind these practices.”
