Humans everywhere use mind-altering substances, from stimulants and narcotics to hallucinogens. Yet surprisingly little is known about how some psychoactive drugs were first discovered and incorporated into daily life. In a study published today, we uncover the prehistoric roots of betel nut chewing. This widespread habit has a long and deep history in the Asia-Pacific region.Betel nut is an addictive stimulant that induces mild euphoria and heightened alertness in users, among other effects, and high rates of mouth cancer among habitual users. After alcohol, caffeine and nicotine, betel nut is the world’s fourth most widely consumed psychoactive substance. Where people chew betel nut. Inset: the Indonesian island of Sulawesi, with two sites with early use of betel nut shown. Adam Brumm / Natural Earth, CC BY Written accounts of betel nut chewing in India and China go back at least 2,000 years. The earliest archaeological evidence dates to around 3,500 years ago, in the form of betel nut chemical compounds found on the teeth of a person who lived in Thailand.Our new study, published in Science Advances, suggests betel nut use originated much earlier than previously believed – perhaps as long as 25,000 years ago. We also found evidence that the modern practice of chewing these palm seeds evolved from an older and simpler form of drug use – one that also carried health consequences.Discovery reveals prehistoric drug useIt all started with our discovery of mysterious grooves in ancient human teeth. Ancient tooth grooves caused by betel nut-sucking, indicated with arrows. A-B: Fragment of an upper jawbone with three molars from a hunter-gatherer who lived around 25,000–16,000 years ago. C-H: The jaws of a hunter-gatherer dated to 7600–6300 years ago. M. Vlok, CC BY During archaeological excavations in South Sulawesi, Indonesia, we unearthed the skeletal remains of two adult hunter-foragers. One we dated to between 25,000 and 16,000 years ago, and the other to between 7,600 and 6,300 years ago. Although they lived at least 10,000 years apart, these individuals shared a common trait: deep, rounded grooves in some of their teeth. At first, this feature greatly puzzled us.The grooves were unlike any previously documented form of prehistoric dental wear. They pointed to an unusual activity, performed repeatedly over a long period. We eventually concluded that the hunter-foragers had regularly held a hard, roughly spherical object between their teeth while sucking on it for extended periods. Over time, the abrasion caused by this activity wore deep grooves into their teeth.In one individual, this dental wear was so extreme that the sensitive pulp chamber, the “living core” of the tooth, had become fully exposed in several places. This would have been very painful.What was the mystery object these foragers were sucking? The grooves reminded us of the “clay pipe facets” seen in people from the colonial period. These were rounded notches worn into the teeth of habitual smokers who regularly clenched the abrasive stems of clay tobacco pipes between their teeth. Top: historical clay pipe. Bottom: rounded notch (clay pipe facet) formed in the teeth of a habitual clay pipe smoker (~1860–1920 CE). M. Langley / M. Vlok, CC BY This led us to consider betel nut. The hard, rounded seeds of the Areca catechu palm generally match the size and shape of the grooves, and habitual betel nut use could explain why these individuals persisted with such a damaging practice. Like clay pipe facets, these telltale tooth marks may have been caused by a long-term drug-related habit. How betel nut chewing beganModern users consume betel by mixing an areca seed (the betel “nut”) with slaked lime – typically made by pulverising burnt shells, limestone, or coral – to form a “quid” that is chewed for its psychoactive effects. Depending on local traditions, other ingredients may also be added. Slaked lime triggers a chemical reaction that allows the nut’s psychoactive compounds to be absorbed more rapidly into the bloodstream. Betel quid chewing in modern New Guinea. It also turns the saliva red. Frequent spitting of this liquid is a characteristic feature of betel quid chewing, and the teeth of long-term users are often permanently stained. A Kol man from East New Britain with teeth stained red from chewing betel quid. International Missions Board, CC BY-NC But chewing betel nut does not result in these distinctive tooth grooves, and the Sulawesi teeth are unstained. We reasoned that, before the development of betel quid chewing as we know it, foragers simply sucked intact betel nuts. Would this have had the same effect? We soaked betel nuts in artificial saliva and tested the resulting extracts on frog egg cells engineered to produce human brain receptors. We found prolonged exposure of intact betel nuts to saliva does release the principal psychoactive alkaloid in these seeds, arecoline. So sucking alone is sufficient to liberate brain-altering compounds. Biomolecular analysis also revealed the presence of arecoline in our ancient foragers’ teeth, confirming they had ingested betel nut. So the results support our hypothesis: early hunter-foragers in Sulawesi were habitually sucking whole betel nuts. Bad habitsWhile the psychoactive “high” of betel nut-sucking may have been milder than that of modern betel quid chewing, the habit was frequent and prolonged enough to dramatically reshape the teeth of its practitioners. One reason for the habit may have been pain relief. Both individuals suffered from chronic dental problems, and arecoline has pain-killing properties. But our findings hint at a cruel irony. The more these people sucked betel nuts, the more damage they inflicted on their teeth. Yet because areca seeds can help dull pain, worsening dental disease may have compelled them to continue the habit.The world’s first habitually used drug?Current models suggest the first traditions of psychoactive drug use, including the production of fermented alcoholic drinks (barley beer), can be linked to the Neolithic advent of farming about 12,500 years ago. Read more: Drugs and religion have been a potent combination for millennia, from cannabis at ancient funerary sites to psychedelic retreats today But betel nut use can now be traced to Ice Age Sulawesi, with the nut-sucking practice emerging by 16,000 years ago, and perhaps as early as 25,000 years ago. This was long before the onset of farming. At some stage, the custom appears to have evolved into the far more potent form of betel quid chewing that remains common today. Betel nut-sucking may be the earliest recorded evidence for habitual drug use. A. Brumm, CC BY-SA The consumption of psychoactive plants is not unique to humans. Neanderthals and other earlier hominins possibly also used medicinal plants.Our study does suggest, however, that the habitual use of some plant drugs has deep roots in our species’ history. What’s more, early hunter-foragers were already experiencing health consequences from long-term use.Adam Brumm receives funding from the Australian Research Council.Fakhri works for Research Center for Archaeometry, Badan Riset dan Inovasi Nasional of Republic Indonesia. Melandri Vlok receives funding from the Wenner Gren Foundation.Carney D. Matheson and Roger Papke do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.