What Do Shrooms Do to Your Brain?

Step 1: Psilocybin becomes psilocin

Psilocybin is the compound mushrooms make and store, but it is not what reaches your brain. After you swallow it, enzymes called alkaline phosphatases in the gut, liver, and blood clip off its phosphate group. What remains is psilocin, a smaller, fat-soluble molecule that crosses the blood-brain barrier easily.¹

Psilocin is also why fresh psilocybin mushrooms often bruise blue when handled. When psilocin is exposed to air after the mushroom is damaged, it oxidizes and links into blue pigment chains, the same chemistry that gives the species its signature color change.²

Step 2: Psilocin activates the 5-HT2A receptor

Serotonin works through at least 14 receptor subtypes. Psilocin binds several of them, but the psychedelic experience depends on one: the serotonin 2A receptor, or 5-HT2A.

The best evidence comes from a classic 1998 experiment. Volunteers who took ketanserin, a drug that blocks 5-HT2A receptors, before taking psilocybin had their psychedelic effects almost completely blocked.³ Later brain imaging confirmed the link from the other direction: the more 5-HT2A receptors psilocin occupied, measured with PET scans, the more intense people rated their experience.⁴

5-HT2A receptors are packed most densely on large neurons in the cortex, especially in areas that handle self-reflection, planning, emotion, and vision. That map explains a lot about what a trip feels like.

Step 3: Rigid brain networks loosen

Your brain runs on large networks that coordinate activity across regions. One of the most studied is the default mode network, or DMN. It is most active when your mind wanders, replays the past, worries about the future, or thinks about yourself. Overactivity in the DMN has been linked to depressive rumination.

Early fMRI work at Imperial College London found that psilocybin reduced activity and connectivity in the DMN's central hubs, and that the drop tracked how strongly people felt their sense of self dissolve.⁵ A 2024 study in Nature that scanned people repeatedly before, during, and after psilocybin found it desynchronized brain networks far more than a stimulant control did, and that a reduced connection between the hippocampus and the DMN persisted for weeks.⁶

At the same time, regions that rarely communicate start exchanging signals. Mapping the whole brain's wiring under psilocybin, researchers found many new, short-lived connections between networks that are usually separate.⁷ Some scientists describe this as the brain temporarily becoming more flexible, or more "entropic," which may make it easier to break out of stuck patterns of thought.

The working theory: psilocybin briefly loosens the brain's habits, which may give therapy a window to build new ones.

Why you see visuals

Psychedelic visuals are not random. Common effects include breathing surfaces, brighter colors, trails behind moving objects, and with eyes closed, intricate geometric patterns.

Two mechanisms likely combine. First, 5-HT2A receptors are abundant in the visual cortex, and activating them changes how visual neurons fire. Psilocybin suppresses alpha brain waves over visual areas, and blocking 5-HT2A prevents both that change and the hallucinations.⁸ Second, a leading model holds that psilocin weakens the thalamus's role as a sensory filter, so more raw, unsorted information reaches the cortex.⁹ Your brain then does what it always does with ambiguous input: it predicts patterns and fills in the gaps, just less constrained than usual.

Why it feels the way it does

The same receptor map explains the emotional side. Psilocin acts heavily on brain regions involved in emotion and self-reflection, which is why people report feelings of connection, awe, or meaning, and also why difficult memories and emotions can surface.

In clinical trials, the intensity of what researchers call a mystical-type experience often predicts how much patients improve afterward.¹⁰ That is one reason studies pair psilocybin with careful preparation, a supportive setting, and follow-up sessions to help people make sense of what came up.

After the trip: new connections

The most exciting finding may be what happens after the drug is gone. Psilocin is cleared within hours, yet benefits in depression trials can last months. Neuroplasticity, the brain's ability to rewire, is the leading explanation.

• In 2018, researchers showed psychedelics promote growth of new dendrites and synapses in cultured neurons, and coined the term psychoplastogens.¹¹
• In 2021, a Yale team imaged living mice and found a single dose of psilocybin increased the density of dendritic spines in the frontal cortex by about 10%, with many new spines still present a month later.¹²
• A 2023 study proposed that psychedelics also bind directly to TrkB, the receptor for the growth factor BDNF, which could help explain the plasticity effect.¹³

Most plasticity evidence so far comes from animals and cell cultures, so how closely it maps onto humans is still being studied.

How long do shrooms last?

The timing follows how quickly psilocybin is converted and cleared:¹

Mushroom potency varies a lot from one batch, and even one mushroom, to the next, which makes the intensity of any given experience hard to predict. Clinical trials use measured, synthetic psilocybin for exactly this reason.

How this differs from antidepressants

SSRIs such as Prozac also work through serotonin, but in a very different way. They raise serotonin levels gradually and are taken every day, often for years, and many people experience emotional blunting. Psilocybin acts directly on one receptor, is given in one or two supervised sessions, and appears to work by temporarily opening the brain to change rather than by steadily adjusting its chemistry. See what the depression trials show.

What scientists still do not know

Researchers are still debating whether the psychedelic experience itself is necessary for the therapeutic benefit. Some labs are developing non-hallucinogenic compounds that keep the plasticity effect without the trip.¹⁴ Others argue that the meaning people find during the experience is central to lasting change. Both camps agree the 5-HT2A receptor is where the story starts.

Common questions

Do shrooms damage your brain?

There is no good evidence that psilocybin damages brain cells at the doses used in research, and it has very low physical toxicity.¹⁵ Its main risks are psychological: panic, confusion, risky behavior while impaired, and in people with a personal or family history of psychosis, the possibility of triggering a psychotic episode.

Is psilocybin addictive?

A formal review for the FDA scheduling process concluded psilocybin has low abuse potential and does not cause compulsive drug-seeking. Tolerance builds within days, so back-to-back use produces much weaker effects.¹⁶

Why do shrooms cause visuals?

5-HT2A receptors are dense in the visual cortex and in circuits that filter sensory input. When psilocin activates them, the brain receives less filtered information and fills in patterns, colors, and movement.

Sources

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2. Lenz C, et al. Injury-triggered blueing reactions of Psilocybe "magic" mushrooms. Angewandte Chemie. 2020. doi.org/10.1002/anie.201910175
3. Vollenweider FX, et al. Psilocybin induces schizophrenia-like psychosis in humans via a serotonin-2 agonist action. NeuroReport. 1998. doi.org/10.1097/00001756-199812010-00024
4. Madsen MK, et al. Psychedelic effects of psilocybin correlate with serotonin 2A receptor occupancy and plasma psilocin levels. Neuropsychopharmacology. 2019. doi.org/10.1038/s41386-019-0324-9
5. Carhart-Harris RL, et al. Neural correlates of the psychedelic state as determined by fMRI studies with psilocybin. PNAS. 2012. doi.org/10.1073/pnas.1119598109
6. Siegel JS, et al. Psilocybin desynchronizes the human brain. Nature. 2024. doi.org/10.1038/s41586-024-07624-5
7. Petri G, et al. Homological scaffolds of brain functional networks. Journal of the Royal Society Interface. 2014. doi.org/10.1098/rsif.2014.0873
8. Kometer M, et al. Activation of serotonin 2A receptors underlies the psilocybin-induced effects on alpha oscillations, N170 visual-evoked potentials, and visual hallucinations. Journal of Neuroscience. 2013. doi.org/10.1523/JNEUROSCI.3007-12.2013
9. Vollenweider FX, Preller KH. Psychedelic drugs: neurobiology and potential for treatment of psychiatric disorders. Nature Reviews Neuroscience. 2020. doi.org/10.1038/s41583-020-0367-2
10. Griffiths RR, et al. Psilocybin produces substantial and sustained decreases in depression and anxiety in patients with life-threatening cancer. Journal of Psychopharmacology. 2016. doi.org/10.1177/0269881116675513
11. Ly C, et al. Psychedelics promote structural and functional neural plasticity. Cell Reports. 2018. doi.org/10.1016/j.celrep.2018.05.022
12. Shao LX, et al. Psilocybin induces rapid and persistent growth of dendritic spines in frontal cortex in vivo. Neuron. 2021. doi.org/10.1016/j.neuron.2021.06.008
13. Moliner R, et al. Psychedelics promote plasticity by directly binding to BDNF receptor TrkB. Nature Neuroscience. 2023. doi.org/10.1038/s41593-023-01316-5
14. Cameron LP, et al. A non-hallucinogenic psychedelic analogue with therapeutic potential. Nature. 2021. doi.org/10.1038/s41586-020-3008-z
15. Johnson MW, Richards WA, Griffiths RR. Human hallucinogen research: guidelines for safety. Journal of Psychopharmacology. 2008. doi.org/10.1177/0269881108093587
16. Johnson MW, et al. The abuse potential of medical psilocybin according to the 8 factors of the Controlled Substances Act. Neuropharmacology. 2018. doi.org/10.1016/j.neuropharm.2018.05.012

This article is for education only and is not medical advice. Psilocybin is a Schedule I substance under U.S. federal law. Talk with a licensed clinician before making decisions about your health.