Incense burners recently unearthed in western China provide new evidence of marijuana’s role in burial rituals, once known only from historic texts.
High in the Pamir Mountains of western China, scientists exploring an ancient cemetery have uncovered 2,500-year old vessels containing the chemical remains of burned cannabis plants.
Cannabis can linger in the human system for a few months at most, but cannabis residue will stick to other surfaces for millennia.
The study suggests cannabis was being smoked at least 2,500 years ago, and that it may have been associated with ritual or religious activities.
Traces of the drug were identified in wooden burners from the burials.
The cannabis had high levels of the psychoactive compound THC, suggesting people at the time were well aware of its effects.
Cannabis plants have been cultivated in East Asia for their oily seeds and fibre from at least 4,000 BC.
But the early cultivated varieties of cannabis, as well as most wild populations, had low levels of THC and other psychoactive compounds.
The evidence was found on 10 wooden braziers containing stones with burn marks that were discovered in eight tombs at the Jirzankal Cemetery site.
The scientists think ancient people put cannabis leaves and hot stones in the braziers and inhaled the resulting smoke.
It's possible the high altitude environment caused the cannabis plants in this region to naturally produce higher levels of THC. There's evidence this can happen in response to low temperatures, low nutrient levels and other conditions associated with high elevations.
The elevated THC levels raise the question of whether the people used wild cannabis varieties with naturally high THC levels or plants bred to be more potent.
An excavated tomb in the Jirzankal cemetery is surrounded by stones in a circular pattern. (Xinhua Wu)
It's the earliest clear evidence of cannabis being used for its psychoactive properties. The plants appear to have been burnt as part of funerary rituals.
The scientists used a method called gas chromatography-mass spectrometry to isolate and identify compounds preserved in the burners.
“What this shows is a close relationship between prehistoric populations and their wild botany,” said Michael Frachetti, an archaeologist at Washington University in St. Louis who was not involved in the work.
To their surprise, the chemical signature of the isolated compounds was an exact match to the chemical signature of cannabis.
Nicole Boivin, director at the Max Planck Institute for the Science of Human History in Jena, Germany, said: "The findings support the idea that cannabis plants were first used for their psychoactive compounds in the mountainous regions of eastern Central Asia, thereafter spreading to other regions of the world."
Humans have long had a complex relationship with cannabis, in part because cannabis is not just one plant with one set of properties. Strains of Cannabis sativa have been used for millennia to produce rope and textiles from the stalks and oil from the seeds.
The excavations dug up more than just THC residue. Notably, analysis of human bones found at Jirzankal revealed that not all of the cemetery’s tenants had been born locally. This hint of ancient immigration supports the idea that the high-elevation Pamirs were once part of the Silk Road, along which goods and traditions passed between geographically distant communities.
The cemetery site is situated near the ancient Silk Road, indicating that the old trade route linking China and the Middle East may have facilitated the spread of marijuana as a drug.
References to drug use, though unverifiable, abound in the historical record. The Greek historian Herodotus, who lived in the fifth century BCE, wrote briefly of the Scythians producing smoke from hemp seeds. The Rig Veda, an ancient Hindu religious text, refers to a mind-altering substance called “soma,” though it’s unclear exactly what it was made of. The Jirzankal Cemetery findings also fit with other ancient evidence for cannabis use at burial sites in the Altai mountains of Russia.
Further research could help give a clearer view of the plant’s ritual significance, but the traces of cannabis left on the braziers from Jirzankal Cemetery are enough to begin “to piece together an image” of cannabis-inflected funerary rites, the new paper’s authors write. The rituals, they think, might have included “flames, rhythmic music, and hallucinogen smoke, all intended to guide people into an altered state of mind.” Call it what you will, but that’s certainly something more than recreational.