Freshly prepared peyote buttons can contain up to 8% of total alkaloids. The previously studied 1000-year-old sample had a lower content, around 2·25%. In our analysis, alkaloid content had fallen to 2%, and mescaline was the only peyote alkaloid we could identify. There was no trace of any of the other tetrahydroisoquinoline alkaloids typical for peyote. Earlier, nicotine and caffeine had been identified in plant remains from a medicine man’s tomb in Bolivia, aged 4 1600 years. Morphine has been found in a 3500 year old ceramic container 5 from Cyprus. From a scientific perspective, the studied peyote material seems to be the oldest plant drug that yielded a major bioactive compound on chemical analysis. From a cultural point of view, our identification of mescaline strengthens the evidence that Native Americans already recognised and valued the psychotropic properties of peyote as long as 5700 years ago.