Mescaline comes from the cactus plant, peyote -- Lophophora williamsii.
Peyote has been used ceremonially for three thousand years by native peoples in Texas and Mexico, where it grows.
Mescaline is structurally similar to the catecholamine neurotransmitters, dopamine and norepinephrine. Predictably, it has some effect on the function of these neurotransmitters, as well as having an effect on the neurotransmitter serotonin.
Peyote was first banned by Europeans in the early 16th Century because of the frightening behavior it caused in users. Its use spread to native tribes in other parts of the U.S. in the late 19th Century. By 1922, there were an estimated 13,000-22,000 ceremonial users of peyote in the U.S.
The active ingredient in peyote, mescaline was first synthesized in 1919. By 1930 over a dozen states had outlawed possession of peyote. Various studies were conducted on peyote/mescaline during the 20th Century. No useful medical application of the drug was found. Peyote/mescaline was banned in the U.S. in 1967 and placed on Schedule I in 1970.
The heads or "buttons" of the cactus are chewed, ground up, or soaked in water and then ingested. Sometimes the powder from ground buttons is sold in gelatin capsules.