People may have smoked marijuana in rituals 2,500 years ago in western China

About 2,500 years ago, mourners gathered in a cemetery in what is now western China to inhale the vapours of burning cannabis plants that came out of small wooden containers. High concentrations of the psychoactive compound THC in these inflamed plants, also known as marijuana, are believed to have caused altered states of consciousness. 

According to a team led by archaeologist Yimin Yang of the Academy of Sciences of China University in Beijing, the Jirzankal cemetery, located in the Pamir Mountains of Central Asia, bears witness to this practice. Chemical residues on wooden burners found in graves provide some of the oldest evidence to date of smoking or inhaling cannabis vapours, reported online researchers on June 12 in Science Advances. Rituals aimed at communicating with the dead or a spirit world probably included cannabis smoking, the team speculates.

Remnants of cannabis of comparable age have been found in several other tombs in Central Asia, including a site in the Altai roller coaster, about 3,000 kilometres northwest of the Pamir Mountains. But the discoveries made at Jirzankal Cemetery offer an unprecedented look at how cannabis was originally used as a psychotropic substance, the researchers say. East Asians had been growing cannabis for at least 6,000 years, but only to consume the oily seeds of the plant and to make clothes and ropes from cannabis fibre. Cannabis varieties grown early in East Asia and elsewhere, like most wild forms of the plant, contained low levels of THC and other psychotropic compounds.

Some of the first evidence of marijuana use comes from the Greek historian Herodotus, who wrote that about 2,500 years ago, in the steppes of Central Asia, about 2,000 kilometres west of the Pamir mountains, cannabis was smoking. But scientists have not known for a long time when and where exactly cannabis plants with a high THC content first developed and which people smoked cannabis for the first time.

According to Robert Spengler, archaeobotanist and co-author of the Max Planck Institute for the Science of Human History study in Jena, Germany, Robert Spengler, the mountain passes of Central and East Asia, including the Pamir region, have hosted trade routes from the First Silk Road, which linked China with West Asia and Europe, which is essential. "Our study suggests that knowledge of the use of cannabis and certain high THC cannabis varieties was among the cultural traditions that spread along the Silk Roads trade routes," Mr. Spengler said at a press conference on June 11.

Archaeological findings indicate that many funeral practices spread in Central and East Asia about 2,500 years ago. For example, smoking cannabis during grave ceremonies was probably part of this process, says archaeologist Michael Frachetti of the University of Washington at St. Louis, who did not participate in the new study. "At that time, the first silk roads linked the people of Beijing to Venice," he says.

Given the new discoveries, the sites in Altai Mountain deserve to be examined more closely to find clues as to the origins of cannabis use," adds archaeologist David Anthony of Hartwick College in Oneonta, N.Y.

To support the Pamir region as a former crossroads, previous chemical analyses of human bones and teeth from the Jirzankal cemetery indicated that 10 of the 34 people tested had grown outside this region. Objects placed in some of Jirzankal's tombs, such as silk fabrics from eastern China and a type of harp from western Asia, suggest that people of widespread cultures have travelled to Central Asia.

Jirzankal Cemetery is located more than 3,000 metres above sea level. Strips of black and white stones extend over the surface of the site. Circular mounds of earth cover the tombs, which are bordered by one or two rings of stones.

Yang's team identified a chemical signature of cannabis on carbonized plant material from 10 wooden burners, or braziers, found in eight Jirzankal tombs. Chemical signs of an abnormally high THC level were found inside nine braziers and on two stones that had been heated and used to burn plants in the braziers.

Yet, these ancient plants would have triggered less powerful psychoactive effects than current cannabis plants grown specifically for high levels of THC, Spengler said.

It is not known whether the people who buried their dead in the Jirzankal cemetery were growing cannabis plants with a high THC content or found a psychoactive variety growing in the wild. In any case, the inhalation of cannabis as part of overwhelming funeral rituals probably began millennia before the cryers gathered on the graves of Frachetti suspects Jirzankal.