“Marijuana can linger in the human system for a few months at most, but cannabis residue will stick to other surfaces for millennia. High up in the Pamir Mountains, in what is now western China, archaeologists were excavating the tombs of Jirzankal Cemetery when they came upon a set of braziers and asked themselves what purpose the tools served. After analyzing the residue, a team of researchers found that it not only came from cannabis, but contained unusually high levels of THC—the compound that gives cannabis its psychoactive, or mind-altering, qualities.”
Full Article:
https://www.theatlantic.com/science/archive/2019/06/ancient-chinese-artifact-has-traces-cannabis-use/591538/