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Muscimol is the isoxazole alkaloid that makes Amanita muscaria, the red-and-white fly agaric, psychoactive. It is not produced by the mushroom directly in quantity; the fresh tissue carries ibotenic acid, which loses carbon dioxide on drying, ageing or heating to give muscimol, so how a sample was handled changes what is in it [4]. Pharmacologically it is a potent and unusually selective agonist at ionotropic GABA-A receptors, the brain's main inhibitory channel, and it has been the reference compound that GABA-A pharmacology is written against for fifty years [1]. It is sold as a research chemical and used in neuroscience as a tool for silencing a brain region reversibly.
- The cleanest available agonist at extrasynaptic delta-containing GABA-A receptors, active near 1 nM
- The reference ligand GABA-A pharmacology is calibrated against
- Parent compound of gaboxadol, tiagabine, nipecotic acid and 4-PIOL
- Reversibly silences a defined brain region, which is why it is a standard neuroscience tool
- Sedation, confusion, ataxia and dissociation; delirium and prolonged sleep at higher exposure
- Fly agaric material also carries ibotenic acid, which is excitotoxic and causes the nausea and agitation
Mechanism
Muscimol is a structural mimic of itself: the isoxazole ring stands in for the carboxylate and the molecule occupies the same orthosteric site on the ionotropic GABA-A receptor, opening the chloride channel and hyperpolarising the cell [1]. That much is ordinary. What is not ordinary is where it binds hardest.
Its highest-affinity targets are the EXTRASYNAPTIC receptors that carry a delta subunit, and the numbers are striking: about 1.6 nM at forebrain alpha4-beta-delta receptors and about 1 nM at cerebellar alpha6-beta-delta, with currents at recombinant alpha4-beta3-delta receptors appearing around 1 to 2 nM [2]. Deleting the delta subunit in mice removes more than half of all high-affinity muscimol binding in the brain and lowers behavioural sensitivity to the drug, which is the knockout showing the binding matters rather than merely existing [2].
That distinction is the whole character of the compound. -A receptors produce brief phasic inhibition when a neuron fires; extrasynaptic delta-containing receptors sit outside the and produce a standing TONIC inhibition set by ambient GABA. A drug that prefers the second at low nanomolar concentrations is turning down a whole region's baseline excitability rather than sharpening individual synaptic events, which is why it reads as heavy, blurred and dissociative rather than as anxiolytic in the way a benzodiazepine does.
⚠️ It is also not simply a sedative, and the exception is worth knowing. Microinjected into the rat pontine reticular formation, muscimol INCREASED wakefulness and reduced both non-REM and REM sleep, as did the delta-selective gaboxadol [3]. Inhibition applied to a region that itself suppresses arousal produces arousal; the direction of the effect depends on which circuit is silenced, not on the drug alone.
Its historical importance is larger than its use. Muscimol was the lead compound from which a family of agents was developed, among them gaboxadol, tiagabine, nipecotic acid and 4-PIOL [1].
receptor fingerprint
-A, extrasynaptic delta (alpha4-beta-delta)agonist
-A, cerebellar delta (alpha6-beta-delta)agonist
-A, (orthosteric site)agonist
Evidencehow good the literature is
The pharmacology is settled and the human clinical evidence is essentially absent, which is an unusual combination and worth stating plainly.
On the receptor side the work is old, deep and consistent. Muscimol has been the standard ionotropic GABA-A agonist since the 1970s and the ligand much of the field's binding work is calibrated against [1]. The delta-subunit selectivity is recent and quantitative, with binding constants near 1 nM and a subunit-knockout confirming that those sites carry most of the high-affinity binding [2].
On the human side there is no controlled trial literature to summarise. What exists is a toxicology record from fly agaric ingestion and a long ethnographic history, neither of which establishes a dose, an indication or a safety margin. The compound's real modern importance is as a laboratory tool and as the scaffold that produced gaboxadol, tiagabine and nipecotic acid [1].
Dosingtypical ranges, not medical advice
interested in protocols and clinical dosages? make an account to see them! ^_^
Safetyrisks and cautions, not medical advice
Muscimol is not a benign supplement and there is no established safe human dose. Amanita muscaria preparations contain a variable mixture of muscimol and ibotenic acid, and the two behave very differently: ibotenic acid is a glutamate-receptor agonist and is excitotoxic, and it accounts for much of the nausea, vomiting, agitation and muscle twitching seen in fly agaric poisoning, while muscimol produces the sedation, confusion and dissociation. Because ibotenic acid converts to muscimol on drying and heating, two preparations of the same mushroom can differ substantially in both potency and character [4]. Reported effects at higher exposures include deep sedation, delirium, ataxia and prolonged sleep. Muscimol should not be combined with alcohol, benzodiazepines, z-drugs or other central depressants, since they act on overlapping inhibitory machinery. Anyone who has taken an unknown quantity of fly agaric material should be assessed medically rather than left to sleep it off.
History
Muscimol was isolated in the 1960s from Amanita muscaria, the fly agaric, whose use in Siberian shamanic practice is among the oldest documented psychoactive traditions. The chemistry that mattered came shortly after: the fresh mushroom carries ibotenic acid, and muscimol is its decarboxylation product, which is why traditional preparations dry or age the material rather than eat it fresh. Through the 1970s and 1980s Danish and Australian groups used muscimol as the starting point for a programme of GABA-mimetic medicinal chemistry, and that programme produced gaboxadol, tiagabine, nipecotic acid and 4-PIOL [1]. Its later career has been as a neuroscience tool: because it silences a region reversibly and predictably, muscimol microinjection became a standard way to ask what a given piece of brain is for.
Resources
This entry is here for reference.
Research
- 2013first citedExtrasynaptic GABAA receptors in rat pontine reticular formation increase wakefulness
- 2023most recentAnalysis of the Ibotenic Acid, Muscimol, and Ergosterol Content of an Amanita Muscaria Hydroalc…
- 1.Muscimol as an ionotropic GABA receptor agonist
- 2.Extrasynaptic δ-GABA(A) receptors are high-affinity muscimol receptors.
- 3.Extrasynaptic GABAA receptors in rat pontine reticular formation increase wakefulness
- 4.Analysis of the Ibotenic Acid, Muscimol, and Ergosterol Content of an Amanita Muscaria Hydroalcoholic Extract with an Evaluation of Its Cytotoxic Effect against a Panel of Lung Cell Lines In Vitro
4 listed here; entry last updated August 2026
Reviews
My notesprivate to this device
FAQ
What is Muscimol?
The isoxazole alkaloid that makes the fly agaric mushroom psychoactive, and the reference agonist at the brain's main inhibitory receptor, GABA-A.
How does it work?
It mimics GABA at the receptor's own binding site and opens the chloride channel. What sets it apart is where it binds hardest: extrasynaptic receptors carrying a delta subunit, at around 1 nM. Those sit outside the synapse and set a standing level of inhibition across a region, rather than shaping individual synaptic events, which is why it reads as heavy and blurred rather than as anxiolytic.
Is it the same as eating fly agaric?
No. The fresh mushroom carries mostly ibotenic acid, which is excitotoxic and causes the nausea, vomiting and agitation; muscimol is what ibotenic acid becomes on drying and ageing. Two preparations of the same mushroom can differ a great deal in both strength and character.
Is it a sedative?
Mostly, but not simply. Injected into one brainstem region in rats it increased wakefulness and cut both non-REM and REM sleep. Inhibiting a circuit that itself suppresses arousal produces arousal, so the direction depends on what is silenced.
Is there a safe dose?
None is established. There is no controlled human trial literature, and the content of mushroom material varies by roughly an order of magnitude with how it was dried and stored.
Limitations of the evidence
- No controlled human trial literature exists; the human record is toxicology and ethnography.
- Muscimol content in mushroom material varies widely with drying and age, so dose is very hard to control.
- The delta-selectivity numbers come from rodent tissue and recombinant receptors, not from humans.
- The wakefulness finding is a region-specific microinjection result and does not describe systemic use.
Adverse effects
- Sedation, confusion, ataxia and dissociation; delirium and prolonged sleep at higher exposure
- Fly agaric material also carries ibotenic acid, which is excitotoxic and causes the nausea and agitation
Notes and cautions
- Ibotenic acid converts to muscimol on drying, ageing and heating; the two have different effects, so preparation changes the experience.
- Silencing a region that itself suppresses arousal can increase arousal; direction depends on the circuit.