How prevalent is mescaline use?

Answer 1

Mescaline use is quite uncommon, because it is hard to cultivate/harvest the cacti containing it, and it is unprofitable to synthesize. Much of the street "mescaline" is actually other psychedelic compounds. It is used in the Huichol religion, but outside of that group it is rarely used, even in comparison to other psychedelics such as psilocybe mushrooms.