A new study has revealed cannabis residue with high levels of THC in ancient funerary incense burners found in western China. The discovery is the earliest evidence of marijuana being burned for its psychoactive properties, as the THC levels found were significantly higher than what is generally seen in wild types of the plant.

There is solid archaeological evidence that humans cultivated cannabis plants at least as far back as 4000 BCE. The plant was primarily harvested for its fibers, making fabric and rope. It is unclear, however, exactly when humans began using the plant for its psychoactive properties, and more specifically when we discovered that burning and inhaling its smoke could induce consciousness-altering effects.

Cannabis is alluded to in the Vedas, ancient Indian religious writings dating as far back as 2000 BCE, but there is little archaeological proof clearly establishing when and how the plant was used. Perhaps the clearest description of cannabis being burned and inhaled came from a text written in 440 BCE by Greek historian Herodotus. The record explains how the Scythians, a nomadic people from the Eurasian region, combusted hemp seeds and subsequently bathed in the smoke.

"The Scythians, as I said, take some of this hemp-seed, and, creeping under the felt coverings, throw it upon the red-hot stones; immediately it smokes, and gives out such a vapour as no Grecian vapour-bath can exceed; the Scyths, delighted, shout for joy, and this vapour serves them instead of a water-bath; for they never by any chance wash their bodies with water," Herodotus wrote nearly 2,500 years ago.

This new study, from an international team of researchers, offers some of the first solid archaeological evidence of cannabis being burned, most likely for its psychoactive effects. The researchers used gas chromatography-mass spectrometry to closely analyze compounds found in ancient wooden burners discovered in funerary tombs from the Pamir mountains in Central Asia.

The tests revealed high levels of a compound called cannabinol (CBN). The primary psychoactive compound in cannabis is THC, however, THC quickly oxidizes into CBN when exposed to air, light or heat. CBD, the other main compound found in cannabis is not psychoactive, and in general if a cannabis plant contains a high level of CBD it will contain a lower level of THC, and vice versa.

So the discovery of primarily CBN in the wooden burners suggests the cannabis used in the prospective ritual was high in THC. Wild cannabis in the region is generally known to not express these high levels of THC so the researchers reasonably hypothesize that either this particular cannabis strain was particularly sourced for its psychoactive qualities or specifically cultivated.

Other artifacts discovered in these ancient tombs, such as harp-like musical instruments, suggest the imbibing of psychoactive cannabis smoke played a part in a larger funeral ritual. The researchers hypothesize in the published paper what these complex religious practices may have consisted of.

"We can start to piece together an image of funerary rites that included flames, rhythmic music, and hallucinogen smoke, all intended to guide people into an altered state of mind," the researchers write in the paper.

Considering this archaeological evidence fits in with the description published by Herodotus nearly 2,500 years ago the researchers suggest this ancient plant knowledge efficiently spread along the trade route known as the Silk Road. Archaeobotanist Robert Spengler, from the Max Planck Institute for the Science of Human History, says this proof affirms Central Asia as a cultural nexus along this all important historical trade route.

"The exchange routes of the early Silk Road functioned more like the spokes of a wagon wheel than a long-distance road, placing Central Asia at the heart of the ancient world," explains Spengler. "Our study implies that knowledge of cannabis smoking and specific high-chemical-producing varieties of the cannabis plant were among the cultural traditions that spread along these exchange routes."

The study was published in the journal Science Advances.

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