Mescaline is a psychoactive substance obtained from plants that can be found in certain varieties of cactus, such as peyote cactus, which has been used by Native Americans for both medicinal and ritual purposes.

Consumption of this substance—which can have adverse effects—extended to Western society in the 19th century, around the time of the birth of psychiatry as a field of medicine. Doctors, thinkers, and artists would use it in numerous experiments.