Psilocin: The Active Metabolite

Psilocin: the molecule that actually does the work

Roughly 30 minutes after psilocybin enters the body, most of what's happening pharmacologically isn't psilocybin anymore. It's psilocin. The two molecules are closely related , psilocybin is essentially psilocin wearing a phosphate group , but that small chemical difference determines almost everything about how the compound moves through the body. Psilocybin is the prodrug. Psilocin is the active form.

Before anything else, the legal position in Australia: psilocybin and psilocin are both listed as Schedule 9 prohibited substances under the Poisons Standard (the document that underpins Australian drug scheduling). Possessing, using, manufacturing or supplying either compound outside of an approved framework is a criminal offence in every Australian state and territory. The only lawful clinical pathway opened since 2023 is via a TGA-approved Authorised Prescriber or the Special Access Scheme, and even then the compound is rescheduled to Schedule 8 (a controlled drug requiring strict controls) solely for those approved clinical contexts. This article is descriptive and educational. Nothing here constitutes advice to seek, obtain, or use either substance.

The chemistry of dephosphorylation

Psilocybin's molecular formula is C₁₂H₁₇N₂O₄P. Psilocin is C₁₂H₁₆N₂O. The difference is a phosphate group (–OPO₃H₂) attached to the hydroxyl position on psilocybin's indole ring. That single addition makes psilocybin chemically stable, less lipophilic, and , critically; unable to cross the blood-brain barrier efficiently on its own.

When psilocybin is ingested, alkaline phosphatase enzymes in the gut wall and liver rapidly cleave that phosphate group in a process called dephosphorylation. What remains is psilocin: a 4-hydroxy tryptamine with high lipophilicity, meaning it crosses biological membranes easily, including the blood-brain barrier. This conversion is part of what pharmacologists call first-pass metabolism, the transformation a compound undergoes before it reaches systemic circulation. The overall pharmacokinetics of psilocin in humans have been characterised in a number of controlled studies, including Franz Vollenweider's group at the University of Zurich and the work published via Johns Hopkins.

Psilocin's plasma half-life in human studies has been reported at approximately 2–3 hours, with most of the compound cleared within 8 hours, predominantly as glucuronide conjugates excreted via the kidneys.

How psilocin interacts with serotonin receptors

Psilocin is a structural analogue of serotonin (5-hydroxytryptamine, or 5-HT). Its primary mechanism involves agonism, meaning it activates rather than blocks; at the 5-HT_2A receptor subtype, which is expressed at high density in cortical regions including the prefrontal cortex. This is distinct from the mechanism of the cannabinoid system (the endocannabinoid system and its receptors like CB1 and CB2), which operates through entirely separate pathways.

Psilocin also shows affinity for other serotonin receptor subtypes, 5-HT_1A, 5-HT_2C, and several others, and has some interaction with dopamine receptors. But the 5-HT_2A agonism is considered the mechanistic centrepiece in the neuroscience literature. Research groups including those at Imperial College London (Robin Carhart-Harris's lab, now at UCSF) have used neuroimaging to describe patterns of altered default mode network activity associated with 5-HT_2A activation under controlled study conditions. That work is documented in peer-reviewed literature, and I'd encourage reading it directly rather than through intermediaries; the primary papers are more careful about what they claim than most coverage of them.

Honestly, I think a lot of popular writing on this topic skips the pharmacology too fast and goes straight to the experiential reports. That's a shame. The receptor-level detail is genuinely interesting and it's where the science is most solid.

Psilocin versus psilocybin: why the distinction matters

The prodrug-to-active-drug conversion matters for several reasons beyond basic pharmacology.

First, bioavailability. Psilocybin's oral bioavailability is reported as reasonably high (studies estimate 50–75% conversion to psilocin under typical conditions), but individual variation in alkaline phosphatase activity means the conversion rate isn't identical across people. Gut microbiome composition, gastric pH, and co-ingestion of food all influence the conversion timeline.

Second, formulation. Because psilocybin is the stable precursor, it is the form typically synthesised for clinical research and any TGA-approved study contexts. Psilocin itself is chemically less stable, oxidising more readily, which makes it harder to work with in pharmaceutical-grade settings. From a Good Manufacturing Practice standpoint, psilocybin is the more tractable starting material.

Third, and this sometimes surprises people, both compounds are separately scheduled under the Poisons Standard. It isn't the case that possession of only one of them sidesteps the law. Both are Schedule 9 prohibited substances in Australian law.

What the research literature actually reports

Clinical studies have reported doses of psilocybin (not psilocin, for the formulation reasons above) in controlled settings, typically in the range described in published protocols from institutions including Johns Hopkins University and NYU Langone. I'm not going to reproduce those figures as a protocol here; the Poisons Standard and Australian criminal law make non-approved use illegal regardless, and presenting dosing details as a how-to serves no legitimate educational purpose in this context.

What the peer-reviewed literature does characterise, descriptively, is a dose-dependent relationship between psilocin plasma concentration and subjective intensity, measured using validated scales like the Altered States of Consciousness questionnaire (the 5D-ASC). A 2020 paper by Holze et al. in Neuropsychopharmacology provided one of the more detailed psilocin pharmacokinetic profiles in healthy participants in a controlled setting, worth reading in full if you're across the primary literature.

Research into psilocin's potential is ongoing, but it's early. Many studies have small sample sizes, lack placebo controls, or involve populations that make generalisation difficult. I'd push back gently against coverage that presents the current evidence base as more settled than it is. The mechanistic science is solid. The clinical evidence is promising but preliminary.

Psilocin's legal status in Australia: the detail

The TGA's 2023 rescheduling decision is frequently described as legalising psilocybin in Australia. That framing is imprecise. What the TGA did was create a narrow, strictly regulated pathway under Schedule 8 of the Poisons Standard, accessible only through:

• An Authorised Prescriber approved by the TGA and the relevant Human Research Ethics Committee, or
• The Special Access Scheme (Category B), for individual patient access under prescriber application.

Outside those pathways, psilocybin and psilocin remain Schedule 9 prohibited substances. Possession, use, cultivation of psilocybin-containing fungi, manufacture, or supply is a criminal offence under both Commonwealth and state/territory law. State penalties vary considerably, Western Australia, where I'm based, carries serious penalties for possession, let alone supply. The ADF (Australian Drug Foundation) maintains accessible, current information on state-by-state legal consequences.

There is no legal avenue for members of the public to access psilocybin or psilocin outside an approved clinical relationship. Anyone claiming otherwise; particularly any operation spruiking retreats or facilitated sessions outside a TGA-registered clinical context, is describing something that is, under Australian law, a criminal enterprise.

A note on the indole structure and related compounds

Psilocin belongs to the tryptamine class of compounds: a large family sharing the indole ethylamine backbone also found in serotonin, melatonin, and dimethyltryptamine (DMT). The 4-hydroxy substitution that distinguishes psilocin from plain tryptamine is shared with a small group of compounds sometimes called the 4-substituted tryptamines, most of which share Schedule 9 status under Australian law. I spent more time than I'd like to admit last winter going through the full Poisons Standard entry by entry, if you haven't read it, the specificity of the scheduling language is striking. Very little is left ambiguous.

I was working through some of this detail at the piano, actually; badly playing a Monk tune while having the scheduling document open on the other screen. Not my most productive afternoon, but the contrast between those two things felt about right for the topic. Complicated structures, formal rules, and a lot of room for misinterpretation.

The science of psilocin is genuinely interesting and the early clinical research is worth following carefully. But the legal framework in Australia is what it is, and education that doesn't lead with that does a disservice to readers.

Sources

• TGA finalises decision on rescheduling psilocybin, Therapeutic Goods Administration
• Magic mushrooms drug facts, Australian Drug Foundation
• Holze et al. (2020), Pharmacokinetics and pharmacodynamics of psilocybin; Neuropsychopharmacology (NCBI/PubMed)
• Poisons Standard (current), Therapeutic Goods Administration

, Daniel Okoro, Psychedelic science & law writer