Mescaline is an alkaloid that is the active hallucinogenic substance of the peyote cactus (Lophophora williamsii), which grows in parts of Mexico and the southwestern United States. The drug is usually taken in capsule form.

The effects of mescaline are similar to those of LSD and include visual and auditory hallucinations, distortions of time sense, feelings of anxiety or even persecution, and feelings of elation.

Not all of these effects necessarily occur because the reaction to mescaline varies considerably among individuals, as well as in the same person at different times. A user's personality, the setting, and the dose all affect the experience.