Mind-altering plants can produce various altered states of consciousness and have thus played important roles in ritual and/or religious activities in various areas of the world (1–4). In prehistoric and early historic Central Eurasia, many plants were used for their secondary compounds, and several are still in prominent use today, notably the opium poppy (Papaver somniferum), ephedra (Ephedra spp.), and cannabis (Cannabis sativa). Plants in the Cannabis genus represent a hybrid complex, with ongoing controversy relating to taxonomy; the lack of taxonomic clarity combined with continual gene flow between wild and domesticated populations has hampered attempts to study the origins and dispersal of this plant (5, 6). Wild cannabis grows across many of the cooler mountain foothills from the Caucasus to western China, especially in the well-watered habitats of Central Asia. However, cannabinol (CBN) levels in most wild cannabis plant populations are low, and it remains a largely unanswered question as to when, where, and how the plant was first cultivated for higher psychoactive tetrahydrocannabinol (THC) production (6). Little is known about the prehistoric use of cannabis outside eastern China, where it was domesticated as an oil-seed crop (7, 8). While recent well-reported and photographed cannabis macroremains have been recovered from burials in the Turpan Basin (ca. 800 to 400 BCE) in northwest China, suggesting shamanic or medicinal uses (9, 10), these discoveries do not adequately reveal how the cannabis plant was used.
Historically, cannabis plants used for ritual and medicinal purposes involved oral ingestion or inhaling the smoke or vapors produced by burning the dried plant. Smoking is defined as the act of inhaling and exhaling the fumes of burning plant material (11) and is today often associated with cigarettes, cigars, and pipes. However, smoking pipes were likely introduced to Eurasia from the New World (12), and no clear evidence exists for them in Central Asia before the modern era. The practice of smoking or inhaling cannabis fumes in ritual and recreational activities was documented in Herodotus’ fifth-century BCE The Histories (13) and was supported by the discovery of carbonized hemp seeds in burials from a handful of sites in Eurasia (1, 14, 15). However, most of the archaeological reports of ancient drug remains were published several decades ago, and re-examination of some of these reports has led to the claims being refuted (discussed below). Modern scientific studies are thus needed to corroborate the remaining reports. Here, we investigated residues from archaeological artifacts recovered in the Pamir Mountains (Fig. 1Opens in image viewer), a region that served as an important culture communication channel through Eurasia, linking ancient populations in the modern regions of China, Tajikistan, and Afghanistan. The chemical analysis reveals ancient cannabis burning and suggests high levels of psychoactive chemicals, indicating that people may have been cultivating cannabis and possibly actively selecting for stronger specimens or choosing plant populations with naturally high terpenophenolic secondary metabolites (6). Alternatively, a process of domestication through hybridization between wild and cultivated subspecies may have inadvertently led to stronger chemical-producing plants through human dispersal and subsequent selection (7).
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