Mescaline: general

Mescaline is a naturally occurring alkaloid found in cacti, including peyote and Trichocereus species [1][2]. It's the only confirmed hallucinogenic phenethylamine known to exist in nature [2]. It works as an agonist at serotonin 5-HT2A/2C receptors, with the hallucinogenic effects driven mainly through 5-HT2A activity [1][2].

Mescaline is one of the oldest hallucinogens, with evidence of use going back 5700 years, and it has played a role in Indigenous religious ceremonies in North America for over five thousand years [1][3]. The mescaline-containing cactus peyote remains the sacramental medicine of the Native American Church [3]. It was first isolated in 1897 by Arthur Heffter, who showed it was solely responsible for peyote's psychoactive effects, and first synthesized in 1919 by Ernst Späth [4].

A mescaline trip can run longer than 12 hours, and you should plan for that: a full day where you can't work, drive, or be responsible for anyone else [5]. Most users seek out the natural cactus form of the drug [5]. Mescaline is not often cut with other drugs and has a different market to street drugs [5].

Intoxication is generally reported as mild and manageable [1]. That's a description of typical experience, not a guarantee for any individual dose or body. Set and setting — who you're with, where you are, what state of mind you're in going in — are, across the psychedelic class, critical determinants of harm [6].

References

1. Mescaline: The forgotten psychedelic — Neuropharmacology (Elsevier)
2. mescaline | Ligand page | IUPHAR/BPS Guide to PHARMACOLOGY — International Union of Basic and Clinical Pharmacology (IUPHAR)
3. Mescaline Therapy Information — UC Berkeley Center for the Science of Psychedelics (BCSP)
4. Mescaline — Wikipedia
5. Mescaline — Drug Science (UK)
6. Hofmann vs. Paracelsus: Do Psychedelics Defy the Basics of Toxicology?—A Systematic Review — PMC / National Library of Medicine