Psilocin: general

Psilocin is the active compound your body produces from psilocybin, the substance in "magic mushrooms" [1]. Most psilocybin-containing mushroom species contain it directly as well [2]. It's a tryptamine alkaloid, and it's the molecule actually responsible for the hallucinogenic effects people associate with these mushrooms [2][3][4]. It works as an agonist at 5-HT2 receptors, part of the serotonin system in the brain [1]. It was first isolated from Psilocybe mexicana by Albert Hofmann and colleagues in 1958, and its structure was worked out and synthesized that same year [5][3][4].

Two things matter most before anything else.

First: psilocin, also called N,N-dimethyl-4-hydroxytryptamine, is a psychoactive substance [5]. Dose is not something this page can tell you — strength varies with source and preparation.

Second: as with classic psychedelics generally, no dose has been established above which life is endangered, and fatal overdose from a pure psychedelic is extremely rare [6][7]. That is not the same as safe. Risk with psychedelics as a class rises with high doses, combining substances, and underlying health conditions, and set and setting — who you're with, where you are, what state you're in — are critical to how the experience goes [6][8]. It is also worth knowing that physiological harm from classic psychedelics at standard doses is generally low, but this says nothing about the psychological intensity of a bad setting or a difficult dose [8].

References

1. psilocin | Ligand page | IUPHAR/BPS Guide to PHARMACOLOGY — IUPHAR/BPS Guide to Pharmacology
2. Psilocin — Wikipedia
3. Psilocin | Effects, Mushrooms, & Regulation | Britannica — Encyclopædia Britannica
4. Psilocin | The Merck Index Online — Royal Society of Chemistry
5. Psilocin - American Chemical Society — American Chemical Society
6. Hofmann vs. Paracelsus: Do Psychedelics Defy the Basics of Toxicology?—A Systematic Review — PMC / National Library of Medicine
7. Understanding Risk in the use of Psychedelics — UC Berkeley Center for the Science of Psychedelics
8. Pharmacological Properties of Psychedelics with a Special Focus on Potential Harms — PubMed