A repeated warning about cannabis use in the post-hippie era is to be aware that what you’re smoking or ingesting isn’t your grandparents’ cannabis. Humans have worked hard in recent decades to produce strains with powerful doses of tetrahydrocannabinol, or THC, the psychoactive component of the plant. The result is a surprisingly intense high that famously sent New York Times columnist Maureen Dowd into a spiral of paranoia after she ingested a cannabis-laced chocolate edible one fateful evening in Colorado.

A superstrong strain of pot might overpower unwitting baby boomers, but all of this might just be a case of déjà vu. Today’s herb could be somewhat like cannabis that people cultivated about 2,500 years ago in Central Asia, a plant also bearing high levels of THC. Research published June 12 in Science Advances offers the first evidence that humans around that time not only used cannabis for the high it offers but also selected strains for their THC-packed psychoactive power, burning them in mortuary rituals. The find represents some of the oldest documented use of cannabis for its mind-altering effects. “I am impressed by this new and important discovery,” says Tengwen Long, an assistant professor and environmental archaeologist at the University of Nottingham, Nimbo campus, who was not involved in the study. “It offers us very important data concerning humans’ close interaction with the plant.”

This earliest example of humans burning cannabis in a purposeful way was uncovered as researchers worked on solving the mystery of ancient wooden burners found at a cemetery site in the Pamir mountain range in eastern China. The burners, dating to about 500 years B.C., were charred. Samples of the char revealed compounds that develop when people living in the region burned cannabis. Furthermore, the estimated levels of THC in these samples were higher than wild cannabis would normally produce, suggesting intentional cultivation of the plant for its psychoactive powers.

Such a discovery adds to growing indications of an association among many cultures of cannabis with the afterworld and death, says Mark Merlin, professor of botany at the University of Hawaii, who was not involved in conducting this study. Cannabis was probably used for “medicinal and spiritual reasons,” he says, “which are not really separated by most traditional societies.”

Although the work shows the earliest chemical evidence of cannabis smoking, says study author Yimin Yang, professor of archaeometry at the University of Chinese Academy of Sciences, it doesn’t necessarily mean that the Pamirs are where the practice first gathered steam. Yang’s co-author Robert Spengler, laboratory director at the Max Planck Institute for the Science of Human History, agrees. Despite a cluster of archaeological finds from the Pamirs and other ancient cultures in the mountain foothill areas of Asia, Spengler urges researchers to continue the quest for earlier examples of cannabis use elsewhere.

More cases may inevitably turn up, says Barney Warf, professor of geography at the University of Kansas, who was not involved in the work. Warf called the most recent finding a “very reasonable and thorough study [that] makes a useful contribution documenting early psychoactive cannabis use. But I would not be surprised if future efforts uncover even earlier cases.”

Other regions where evidence of ancient cannabis use has emerged include the lands of the ancient Scythians in Siberia and similarly old sites in China, where hints of recreational use have been discovered, says study author Hongen Jiang, professor of archaeobotany at the University of the Chinese Academy of Sciences. Merlin points to the discovery in Japan of seeds that are about 10,000 years old. “This was a key plant in Eurasia,” he says.

A practice involving cannabis and death rites that may have disseminated far and wide along trade routes such as the Silk Road could have met its end with the rise of monotheism, Merlin says. “The spread of the major monotheistic religions pretty much wiped out shamanism, but there are vestiges,” he notes.

This sense of an ancient diversity of human ritualistic use lends context to the attention cannabis receives in contemporary headlines, says Spengler. “It is important to continually illustrate that the human interaction with this plant goes deeper back in time,” he says.

In the meantime, Long sees the findings reported in this study as “unambiguous” in confirming early use of cannabis deliberately as a psychoactive substance. Merlin agrees that all signs point to intentional use of the plant for this purpose, but it’s also possible that ancient people burned it to mask the smell of death and decay associated with mortuary rites, he says.

Still, Merlin doesn’t think that’s really the case, because of the link of cannabis to the burials of shamans, suggesting shamans might continue their practices in the afterlife. Merlin himself has seen a another example of ancient cannabis use, although without confirmation of burning. “It was almost two pounds of cannabis next to a shaman’s head, practically still green,” he says, expressing awe of the find in tombs in Turpan, northwest China. “I observed this 2,500-year-old shaman, and he had mortar that had been caked in cannabis with him. That was a remarkable find.”