Psilocin

Psilocin (4-hydroxy-N,N-dimethyltryptamine; 4-HO-DMT) is the pharmacologically active metabolite of psilocybin, the phosphorylated prodrug isolated by Albert Hofmann and colleagues at Sandoz in 1958 from the Mesoamerican ceremonial mushroom Psilocybe mexicana. Structurally, psilocin is a 4-hydroxylated indole tryptamine that differs from the endogenous neurotransmitter serotonin only by a shift of the hydroxyl group from the 5- to the 4-position and by the presence of two N-methyl groups. The compound acts as a non-selective serotonin receptor agonist with highest functional relevance at the 5-HT2A receptor, where it activates Gq-coupled phospholipase signaling in layer V cortical pyramidal neurons to produce the characteristic perceptual, cognitive, and affective alterations that define the psychedelic state. Psilocin also binds with meaningful affinity to the 5-HT2C, 5-HT1A, 5-HT2B, and 5-HT7 receptors, and recent work has identified direct, high-affinity binding to the transmembrane domain of the TrkB neurotrophin receptor with an affinity approximately 1,000-fold greater than that of conventional antidepressants, promoting BDNF-dependent dendritic spine growth and synaptic remodeling that persists weeks beyond the acute pharmacological window.

Following oral administration of psilocybin, first-pass dephosphorylation by intestinal alkaline phosphatase liberates psilocin, which is absorbed with an oral bioavailability of approximately 52.7 percent and reaches peak plasma concentrations at 1.8 to 4 hours. The elimination half-life ranges from 2 to 5 hours, with metabolism proceeding through three principal routes: UGT1A10-mediated O-glucuronidation (the dominant pathway in vivo, producing psilocin-O-glucuronide at plasma concentrations approximately four-fold higher than those of free psilocin), MAO-A-catalyzed oxidative deamination to 4-hydroxyindole-3-acetic acid (4-HIAA, accounting for approximately 33 percent of urinary recovery), and CYP2D6- and CYP3A4-mediated oxidation and demethylation that produce minor metabolites including a putative oxidized psilocin derivative and norpsilocin. Unlike tropisetron and other CYP2D6-dependent compounds, clinical studies have not demonstrated a significant influence of CYP2D6 genotype on psilocin plasma concentrations in human subjects.

The clinical evidence base for psilocybin (administered as the prodrug with psilocin as the effector) has expanded substantially since 2016. COMPASS Pathways successfully achieved the primary endpoint in both pivotal Phase 3 trials of COMP360 psilocybin for treatment-resistant depression, confirming consistent efficacy across 839 patients, and the compound holds FDA Breakthrough Therapy designation for this indication. Randomized trials at Johns Hopkins and NYU demonstrated that a single high-dose psilocybin session produced sustained reductions in depression and anxiety in 80 percent of patients with life-threatening cancer, with effects persisting six months or longer. Open-label and controlled studies have reported clinically meaningful signals in tobacco smoking cessation (60 percent biologically verified abstinence at 30 months), alcohol use disorder, obsessive-compulsive disorder, and cluster headache. Preclinical work has established that psilocin promotes rapid and persistent dendritic spine growth in the medial prefrontal cortex, ameliorates chronic stress-induced neuroplasticity deficits through BDNF-mTOR pathway activation, and suppresses inflammatory signaling.

The safety profile is characterized by transient, dose-dependent cardiovascular effects (systolic blood pressure elevation to 140 to 155 mmHg, moderate tachycardia), self-limiting psychological distress during the acute session, and a theoretical concern regarding 5-HT2B receptor-mediated cardiac valvulopathy with chronic or frequent dosing. The compound has no established physical dependence liability, no withdrawal syndrome, and an extremely wide acute toxicity margin. Contraindications include concurrent lithium therapy, active psychotic disorder, and unmonitored combination with monoamine oxidase inhibitors. Psilocin and psilocybin are classified as Schedule I substances under the United Nations Convention on Psychotropic Substances and under United States federal law; research use requires DEA Schedule I researcher registration and institutional authorization. This monograph reviews the chemistry, synthesis, and structural pharmacology of psilocin; the multi-receptor mechanism and TrkB-dependent neuroplasticity; comprehensive pharmacokinetics; the clinical evidence base across all studied indications; sourcing and quality considerations for research-grade material; reconstitution and handling; stack-interaction considerations; adverse events and safety; and a comparative assessment of five serotonergic psychedelic compounds against psilocin on five competency standards.