The Entropic Brain: Psilocybin, Disorder, and Healing

Psilocybin Entropic Brain Theory & REBUS Model

3x greater neural disruption

Psilocybin produced more than threefold greater acute disruption of brain connectivity than methylphenidate, and left connectivity between the anterior hippocampus and the default mode network reduced for weeks afterward.

Siegel et al., Nature, 2024

2014

year the entropic brain theory was published

N=11

healthy volunteers in the first test of REBUS's psychological assumptions (Zeifman 2025)

Nature Medicine

network integration increase correlates with depression response

Siegel et al., Nature, 2024

View as image ↗

The premise seems backward: psilocybin may help people heal by making their brains temporarily more disordered. Yet a decade of neuroscience research points toward exactly that conclusion. When Siegel et al. measured brain connectivity under psilocybin in a 2024 Nature study, they found more than threefold greater disruption than a stimulant control drug, concentrated in the default mode network — the system most associated with our sense of space, time, and self. Weeks after the session, one specific connection remained changed. Psilocybin neural disorder healing is not a metaphor. It is a measurable brain event, though the link from that event to clinical recovery is still being assembled study by study.

Understanding why this might work requires stepping back to a 2014 theory that reframed how neuroscientists think about both consciousness and psychiatric illness. The default mode network's role in psilocybin therapy is one piece of this story. The entropic brain hypothesis is the broader framework that explains what the entire brain is doing during and after a therapeutic psilocybin dose.

The Sub-Critical Brain: Why Depression May Be Too Ordered, Not Too Chaotic

The conventional picture of a depressed brain emphasizes abnormality without specifying what kind. Carhart-Harris's 2014 theory paper offered a more precise vocabulary for the question: the brain can be described by how unpredictable its activity is, and psychiatric rigidity may sit at the low end of that scale.^[1]

The theory's organizing concept is criticality: the transition zone between rigid order and total disorder, where certain signatures such as power-law scaling appear. Carhart-Harris's argument in 2014 contained a nuance that popular retellings usually drop. He did not claim that criticality is simply the ideal and that more entropy is always better. He argued that entropy is suppressed in normal waking consciousness — that we operate just below criticality — and that this suppression is what furnishes ordinary experience with its constrained, reliable quality, including metacognition, reality-testing, and a stable sense of self.^[1]

Entropy suppression, in other words, is a feature. The proposal is that in certain conditions it becomes excessive. In depression, the default mode network runs a narrow loop of self-referential negative thought. In OCD, specific circuits fire in relentless repetition. In addiction, responses to drug cues override flexible decision-making. These conditions look different on the surface, but the framework describes them as converging on the same quality: a repertoire that has narrowed too far.

When Carhart-Harris revisited the hypothesis four years later, he reported that the core empirical claim — elevated entropy under psychedelics — had accumulated support from separate and independent studies and analyses, alongside evidence for greater brain criticality. That paper also made the clinical ambition explicit, proposing the framework as a tool for describing and informing treatment of psychiatric and neurological conditions such as depression.^[2]

The Nuance Popular Retellings Drop

Entropy Is a Band, Not a Direction

The entropic brain hypothesis is usually summarised as “more entropy is better.” It says something more specific: normal waking consciousness sits deliberately below criticality, and there are limits at both ends past which consciousness may be lost.

Sub-critical / rigid

Depression · OCD · Addiction

The repertoire of states has narrowed too far. The next moment is highly predictable — a loop rather than a search.

Normal waking consciousness

Just below criticality

Entropy is actively suppressed here, and that suppression is a feature: it buys reality-testing, metacognition and a stable sense of self.

Criticality

The psychedelic state

The transition zone between order and disorder. A greater repertoire of connectivity motifs forms and fragments across time.

Beyond the upper limit

Disorganisation

The hypothesis sets an upper bound as well as a lower one. Past either limit, consciousness may be lost.

Band positions and widths are conceptual. The hypothesis specifies an ordering along this axis, not measured entropy values, and no study has placed a clinical population on it numerically. The therapeutic proposal is a temporary move toward the middle-right of this band — not a permanent relocation, and not a claim that further right is always better.

Carhart-Harris 2014, Frontiers in Human Neuroscience [1]; Carhart-Harris 2018, Neuropharmacology [2]

The First Measurement: MEG Signal Diversity Under Psychedelics

The entropic brain theory needed direct measurement, and Schartner et al. supplied the first in 2017.^[3]

Using magnetoencephalography (MEG), which captures the magnetic fields generated by neural firing, Schartner's team computed signal-diversity measures — entropy and Lempel-Ziv complexity — on spontaneous brain activity from participants who had received psilocybin, ketamine, or LSD. Signal diversity serves as a proxy for entropy: how varied the brain's activity patterns are from moment to moment.

All three drugs produced reliably higher spontaneous signal diversity than placebo, and the effect survived controlling for spectral changes, ruling out the most obvious confound. The increase was most pronounced for single-channel Lempel-Ziv complexity, meaning the effect was strongest in temporal rather than spatial signal diversity. The team also found selective correlations between the change in signal diversity and participants' reports of how intense the experience was.

The result mattered for a specific reason the authors emphasized: this was the first time these measures had been applied to the psychedelic state, and crucially, the first time they had yielded values exceeding normal waking consciousness. Prior work had established that these measures score lower under anesthesia than in wakeful rest. Psychedelics pushed them in the opposite direction, past the waking baseline.

Direct Measurement

Schartner et al. (2017) · Scientific Reports

Population

Healthy volunteers, MEG recordings pooled across three existing psychedelic datasets

Intervention

Psychoactive doses of psilocybin, ketamine, or LSD

Comparator

Placebo

Finding

All three drugs produced reliably higher spontaneous MEG signal diversity than placebo, exceeding normal waking values and surviving control for spectral changes. The increase was largest for temporal (single-channel Lempel-Ziv) diversity, and correlated selectively with reported experience intensity.

positive Establishes that the entropy increase is real and measurable across three chemically distinct drugs. Does not test dose-response — each drug was given at a single psychoactive dose.

Schartner et al., Scientific Reports, 2017

One further point is worth drawing out. Psilocybin acts primarily through serotonin 2A receptors; ketamine works through NMDA glutamate receptors. That two such different pharmacological routes converge on the same signal-diversity signature suggests the entropy increase is a property of the state rather than a quirk of one receptor profile.

What Happens Inside a Depressed Brain After a Psilocybin Session

Carhart-Harris led a 2017 open-label study examining what psilocybin does to the brains of people who had not responded to conventional antidepressants.^[4]

Nineteen patients with treatment-resistant depression received two psilocybin doses (10 mg, then 25 mg a week later) alongside psychological support. fMRI measured cerebral blood flow and resting-state functional connectivity before treatment and again one day after the 25 mg dose. Usable pre- and post-treatment scans were obtained from 16 of the 19.

The timing matters, and it is where secondhand accounts of this study most often go wrong. These are post-treatment measurements taken the day after the session — not recordings of the acute experience. Whole-brain analysis showed decreased blood flow in the temporal cortex, including the amygdala, the region central to processing threat. The size of that amygdala decrease correlated with the reduction in depressive symptoms.

The connectivity findings are more specific than they are usually reported. Resting-state connectivity within the default mode network increased after treatment. Two connections predicted clinical response at five weeks, and they moved in opposite directions: increased connectivity between ventromedial prefrontal cortex and bilateral inferior lateral parietal cortex, and decreased connectivity between parahippocampal and prefrontal regions. There is no general "increase in hippocampal connectivity" here — the predictive parahippocampal finding runs the other way.

Depressive symptoms fell in all 19 patients at one week, and 47% met criteria for clinical response at five weeks — a notable rate in a group that had not responded to at least two prior antidepressants. The authors noted that these post-treatment brain changes differ from the acute effects of psychedelics, and proposed a "reset" mechanism to describe the pattern.

The design was open-label: patients knew what they were receiving, and there was no control group, so the clinical numbers cannot be separated from expectancy. What the study contributes is the imaging: objective, next-day brain changes in depressed patients that tracked their outcomes.

How the REBUS Mechanism Explains Beneficial Disorder

By 2019, Carhart-Harris and Friston had developed a more mechanistic account of why an entropy increase might be therapeutic.^[5]

REBUS — Relaxed Beliefs Under pSychedelics — integrates the entropic brain hypothesis with the free-energy principle and predictive coding. In that framework the brain is a prediction machine: high-level regions continuously generate predictions ("priors") and send them downward, while prediction errors travel upward and drive belief updating.

Precision weighting determines how confidently a prediction is held. A high-precision prior is held rigidly and resists revision. The REBUS proposal is that psychedelics, via their entropic effect on spontaneous cortical activity, relax the precision of high-level priors — liberating bottom-up information flow, particularly from intrinsic sources such as the limbic system.

Carhart-Harris and Friston extended this beyond mental health, suggesting the same process could revise other heavily weighted priors, including entrenched political, religious, or philosophical positions. It is a theoretical paper: it assembles existing evidence into a unified model rather than testing new predictions.

For a deeper treatment of REBUS, including the first empirical test of its predictions, see REBUS Model: How Psilocybin Relaxes the Brain's Beliefs.

After the Chaos: How Integration Follows Disruption

The short-term picture is disruption. The subacute picture is integration, and it is a different thing entirely.

Daws et al. published a 2022 Nature Medicine analysis spanning two clinical trials of psilocybin for depression.^[6] The first was an open-label trial in treatment-resistant depression, with fMRI at baseline and one day after the 25 mg dose. The second was a double-blind randomized controlled trial comparing psilocybin therapy against escitalopram, with fMRI at baseline and three weeks after the second psilocybin dose.

In both trials the antidepressant response was rapid and sustained, and in both it correlated with decreases in fMRI brain network modularity. Modularity measures how strongly networks maintain distinct functional boundaries. High modularity means segregated, rigid organization. Lower modularity means networks communicate more freely across those boundaries — a global increase in integration. Network cartography analyses added a mechanistic detail that connects directly back to pharmacology: it was specifically the 5-HT2A-receptor-rich higher-order networks that became more interconnected and more flexible after treatment.

The critical comparison came from the escitalopram arm of the second trial. Escitalopram produced a milder antidepressant response — and no changes in brain network organization at all. A drug that works by gradually adjusting serotonin reuptake did not reorganize brain networks the way a single high-entropy session did.

That dissociation is the strongest argument in this literature that psilocybin's mechanism is not simply serotonin modulation. It points to network-level reorganization that the entropic disruption enables. The chaos is not the end state; it is a transition.

The Strongest Neuroimaging Dataset Yet: What the 2024 Nature Study Found

Siegel et al. published what is probably the most technically precise psilocybin neuroimaging study to date in Nature in 2024.^[7] Rather than averaging across a large group, the team used longitudinal precision functional mapping: a small number of healthy adults (six with complete data) scanned roughly 18 times each, before, during, and for three weeks after 25 mg psilocybin and 40 mg methylphenidate, then brought back 6–12 months later for a replication dose.

Mapping each person's individual network architecture first, then measuring how psilocybin disturbed that architecture, avoids the blurring that group-average studies impose.

The headline result: psilocybin massively disrupted functional connectivity in cortex and subcortex, acutely producing more than threefold greater change than methylphenidate. The mechanism behind that number is desynchronization across spatial scales. Psilocybin reduced correlations within networks and anticorrelations between networks simultaneously — pushing both of the quantities that define a network boundary toward zero, which dissolves the distinction between networks rather than adding new connections.

These changes were strongest in the default mode network, which the authors note is connected to the anterior hippocampus and is thought to underlie our sense of space, time, and self. Individual differences in the magnitude of connectivity change were strongly linked to the subjective psychedelic experience. In a neat demonstration that the state is not fixed, having participants perform a perceptual task reduced the psilocybin-driven connectivity changes.

The persistent finding is the one that matters most for the healing question. Psilocybin caused a lasting decrease in connectivity between the anterior hippocampus and the default mode network, still present weeks later. The authors propose this reduction as a possible neuroanatomical correlate of the proplasticity and therapeutic effects of psychedelics — a hypothesis this study raises rather than confirms, since the participants were healthy volunteers and the study did not measure clinical or well-being outcomes at follow-up.

For a focused treatment of the entropy measurement evidence, see How Psilocybin Increases Brain Entropy (And Why That's Good).

Disruption Is Not Damage — It Is a Timeline

What Was Measured, and When

The damage question turns entirely on timing, and the windows in this literature are routinely collapsed. Each row below is pinned to the study that actually scanned at that interval — including what that study did not look at.

During the session

Acute dosing window

Acute

• ●Functional connectivity massively disrupted in cortex and subcortex — more than threefold greater change than methylphenidate, driven by desynchronization and strongest in the default mode network.^[7]
• ●MEG signal diversity rises above normal waking values under psilocybin, ketamine and LSD, correlating with reported experience intensity.^[3]
• ●EEG entropy correlates with an acute decrease in confidence in negative self-beliefs (25 mg, not 1 mg).^[8]

Not measured: No study has tracked how long entropy itself stays elevated once the acute effects fade.

Next day

~24 hours

Post-acute

• ●In 19 treatment-resistant patients (16 with usable scans): decreased temporal-cortex blood flow including the amygdala, correlating with symptom reduction. Connectivity within the DMN increased.^[4]
• ●Trial 1 of the Daws analysis scanned here: decreased brain network modularity, correlating with antidepressant response.^[6]

Not measured: These are post-treatment scans, not recordings of the acute state — a distinction frequently lost in summaries.

Three weeks

21 days

Persistent

• ●Trial 2 of the Daws analysis scanned here: same decreased-modularity pattern; 5-HT2A-rich higher-order networks more interconnected and flexible. Escitalopram arm showed no network change.^[6]
• ●Anterior hippocampus–DMN connectivity remains reduced. Proposed by the authors as a possible correlate of proplasticity and therapeutic effect.^[7]

Four weeks

28 days

Persistent

• ●Reduced confidence in negative self-beliefs persists, and tracks increases in well-being — the strongest relationship in that dataset. In 11 healthy volunteers.^[8]

Not measured: Siegel 2024 studied healthy volunteers and did not measure well-being or clinical outcomes at follow-up, so the brain finding and the well-being finding come from different studies.

Six to twelve months

Long term

Largely unmeasured

• ●Participants returned for a replication dose at this interval, establishing that the acute effect reproduces within the same individuals.^[7]

Not measured: Connectivity was not continuously tracked across the intervening months. Whether the hippocampal–DMN reduction resolves, persists or rebounds is unmeasured.

The shape of this timeline — large temporary disruption, then reorganisation that correlates with getting better — is the opposite of what a neurotoxic compound produces. It is not, on its own, evidence of long-term safety: the rows thin out quickly after four weeks.

Schartner 2017 [3]; Carhart-Harris 2017 [4]; Daws 2022 [6]; Siegel 2024 [7]; Zeifman 2025 [8]

Testing the Psychological Half: Belief Revision at Four Weeks

Siegel 2024 established what the brain does. It did not test whether that translates into psychological change, because it did not follow well-being. Zeifman et al. published a 2025 study aimed squarely at that gap.^[8]

Eleven healthy volunteers received 1 mg and 25 mg psilocybin four weeks apart. Confidence ratings for personally held beliefs were collected before, during, and four weeks after each dose. The team measured acute EEG entropy and subjective effects, and well-being before and four weeks after.

Confidence in negative self-beliefs decreased following the 25 mg dose. EEG entropy and subjective effects under 25 mg both correlated with that decrease — acutely and at four weeks. The strongest relationship in the dataset was between decreasing confidence in negative self-beliefs and increasing well-being.

The authors describe this as the first empirical evidence that relaxation and revision of negative self-belief confidence mediates psilocybin's positive psychological outcomes, and as tentative evidence for a neuronal mechanism in increased neuronal entropy. They named the extended framework REBAS — Revised Beliefs After pSychedelics — capturing the claim that beliefs are not merely relaxed during the session but revised afterward, and that the revision holds for at least four weeks.

Their own framing is deliberately restrained: a preliminary examination of two psychological assumptions of REBUS, in healthy volunteers rather than patients, with an explicit statement that replication in larger and clinical samples is necessary.

This connects to the clinical outcomes literature: for how this mechanism translates to depression remission rates, see Psilocybin for Depression: Results from the Largest Clinical Trials.

Where the Causal Chain Breaks

No Single Study Measures Entropy and Recovery Together

The proposed chain runs entropy increase → belief revision → recovery. Read the two middle columns down the page: the studies that measured entropy directly were run in healthy volunteers, and the studies run in patients did not measure entropy at all.

Study	Who	Entropy measured?	Outcome measured?	What it licenses
Carhart-Harris et al.[1] 2014 · Front. Hum. Neurosci.	Theory paper	○ No Interprets existing neuroimaging	None — no new data	Supplies the framework and the vocabulary. Generates predictions; tests none of them.
Schartner et al.[3] 2017 · Scientific Reports	Healthy volunteers	● Yes MEG entropy + Lempel-Ziv	Experience intensity only	Establishes the entropy increase is real, replicates across three drugs, and exceeds waking baseline. Says nothing about therapy.
Carhart-Harris et al.[4] 2017 · Scientific Reports	19 treatment-resistant patients	○ No Blood flow + connectivity	47% response at 5 weeks	First post-treatment imaging in depressed patients, with changes that tracked outcomes. Open-label with no control arm, so the clinical numbers carry expectancy.
Daws et al.[6] 2022 · Nature Medicine	Two depression trials	○ No Network modularity	Antidepressant response	The strongest specificity evidence in the set: network reorganisation tracked response and was absent in the randomised escitalopram arm.
Siegel et al.[7] 2024 · Nature	6 healthy adults, ~18 scans each	◉ Proxy Desynchronization, not an entropy metric	No follow-up well-being measure	The most precise map of what psilocybin does to network architecture, and the persistent hippocampal–DMN finding. Cannot speak to clinical benefit — it did not measure any.
Zeifman et al.[8] 2025 · Scientific Reports	11 healthy volunteers	● Yes Acute EEG entropy	Well-being at 4 weeks	The closest thing to an end-to-end test: entropy, belief change and well-being in one design, with 1 mg vs 25 mg separation. Preliminary, healthy volunteers, N=11.

This is a convergent, dose-separated, multi-study pattern — not proof of causation. Closing the gap would take a clinical sample in which entropy, belief change and symptom outcome are measured in the same participants, or a design that manipulates entropy independently of the rest of the psychedelic experience. Neither exists yet.

Carhart-Harris 2014 [1]; Schartner 2017 [3]; Carhart-Harris 2017 [4]; Daws 2022 [6]; Siegel 2024 [7]; Zeifman 2025 [8]

Does Psilocybin Damage the Brain? A Direct Answer

The question appears frequently in search data, and the entropic brain evidence speaks to it directly.

Damage implies lasting harm. What the imaging evidence documents is large but temporary disruption, followed by measurable reorganization. Daws et al. (2022) found decreased network modularity after treatment, and the size of that shift tracked antidepressant response — a change correlated with getting better, not worse. Siegel et al. (2024) found acute disruption that resolved, leaving one specific connection — anterior hippocampus to DMN — reduced for weeks, which the authors interpret as a plausible correlate of therapeutic plasticity rather than injury.

The timing pattern of temporary disruption followed by durable reorganization is the opposite of what a neurotoxic compound would produce. No neuroimaging study of therapeutic psilocybin doses has documented structural damage. That said, "no structural damage found" is a statement about what has been looked for and measured, not a guarantee about every exposure pattern.

Who This Evidence Does Not Cover

Moderate

Controlled-trial findings do not generalize to unsupervised use

Concern

The entropic brain literature is built almost entirely on single or double doses given in controlled clinical settings with screening, preparation, and psychological support. Repeated unsupervised high-dose use is a different exposure pattern that these studies did not measure. Separately, a high-entropy brain state carries genuine risk for people with a personal or family history of psychosis or bipolar disorder — a question distinct from structural damage, and one that clinical trials address by excluding those participants.

What the research says

Read these findings as evidence about supervised therapeutic dosing in screened participants. They do not establish safety for recreational, repeated, or unscreened use, and the exclusion criteria used in the trials are themselves informative about who was never studied.

Particularly relevant for: People with personal or family history of psychosis or bipolar disorder; anyone considering unsupervised use

What to do

Discuss any psychedelic use with a qualified clinician who knows your psychiatric and family history. This article is research education, not medical advice.

Siegel et al., Nature, 2024; Carhart-Harris et al., Scientific Reports, 2017; Zeifman et al., Scientific Reports, 2025

What the Research Cannot Yet Confirm

The evidence arc from 2014 to 2025 is substantial, and several important questions remain open.

How long entropy itself stays elevated is poorly characterized. Most studies measured entropy acutely, during the session. The network changes Daws et al. measured were documented at one day post-dose in the first trial and three weeks in the second. Siegel et al. tracked connectivity for three weeks and found a persistent hippocampal–DMN reduction, but connectivity is not the same measurement as entropy. Whether entropy remains elevated for hours or days after a session is not well established.

Sample sizes are small. Zeifman 2025 had 11 participants; Siegel 2024 analyzed six. Precision functional mapping trades breadth for depth deliberately, and the depth is real — roughly 18 scans per person. But effect sizes from very small samples often shrink in larger replications, and Zeifman's team states plainly that replication in larger and clinical samples is necessary.

Most of the mechanism work is in healthy volunteers. Siegel 2024 and Zeifman 2025 both studied healthy participants. The patient imaging comes from Carhart-Harris 2017 and Daws 2022, neither of which measured entropy directly. The chain that runs entropy → belief revision → clinical recovery has not been measured end-to-end in a single clinical sample.

The causal claim is not yet established. The supporting data are consistent, converge across labs and methods, and in Zeifman 2025 show the expected dose separation between 1 mg and 25 mg. That is a strong correlational case. Establishing causation would require manipulating entropy independently of the rest of the psychedelic experience, which no study has yet done.

For the full theoretical framework, see The Entropic Brain Theory: Robin Carhart-Harris's Framework. For how entropy connects to cognitive flexibility and mental health more broadly, see Entropy and Mental Health: Why a More Flexible Brain Is Healthier.

The Bottom Line

A decade of research supports a counter-intuitive proposition: psilocybin may heal in part by temporarily increasing neural disorder. The entropic brain theory (Carhart-Harris 2014, revisited 2018) frames normal waking consciousness as deliberately sub-critical, with psychiatric conditions representing a repertoire that has narrowed too far. Signal-diversity measurements (Schartner 2017) confirmed that psychedelics push brain activity past normal waking values, and precision neuroimaging (Siegel 2024, Nature) showed the mechanism is desynchronization — more than threefold greater acute disruption than methylphenidate, strongest in the default mode network, leaving anterior hippocampus–DMN connectivity reduced for weeks. Post-treatment network integration increases correlate with antidepressant response and are absent after escitalopram (Daws 2022, Nature Medicine). The first test of REBUS's psychological assumptions (Zeifman 2025) found that EEG entropy tracked decreasing confidence in negative self-beliefs, which in turn tracked well-being at four weeks. The evidence is convergent and dose-separated, but remains correlational, drawn largely from healthy volunteers, and built on small samples.

Frequently Asked Questions

Does psilocybin cause permanent brain changes?

Post-treatment imaging shows changes that outlast the session, but they appear beneficial rather than damaging. Daws et al. (Nature Medicine, 2022) found decreased brain network modularity after psilocybin therapy, correlated with antidepressant response. Siegel et al. (Nature, 2024) found reduced connectivity between the anterior hippocampus and default mode network persisting for weeks. "Permanent" is not established in either direction: Siegel's team scanned for three weeks and brought participants back 6–12 months later for a further dose, but no study has continuously tracked brain connectivity across the intervening months.

How does neural disorder help with healing?

The entropic brain framework proposes that depression, OCD, and addiction involve a brain cycling through a repertoire that has narrowed too far. A temporary entropy increase disrupts those fixed patterns and, according to the REBUS model, relaxes the precision weighting of rigid self-beliefs that maintain them. Zeifman et al. (2025) provided the first direct psychological test: EEG entropy during a 25 mg psilocybin session correlated with decreased confidence in negative self-beliefs, and that decrease persisted at four weeks and tracked improvements in well-being.

What does psilocybin do to brain networks?

It desynchronizes them. Siegel et al. (2024) found psilocybin simultaneously reduced correlations within networks and anticorrelations between networks, dissolving the statistical boundaries that define a network — more than 3x greater connectivity change than methylphenidate, strongest in the default mode network. In the subacute window, Daws et al. (2022) found decreased network modularity, meaning previously segregated networks communicated more freely, with 5-HT2A-receptor-rich higher-order networks becoming the most interconnected and flexible. That post-treatment pattern correlated with antidepressant response and was not produced by escitalopram.

Does psilocybin damage the brain?

The available evidence does not support a brain damage conclusion. Psilocybin causes temporary, large-scale disruption of brain connectivity, but post-acute measurements show reorganization that correlates with clinical improvement rather than degradation. No neuroimaging study of therapeutic psilocybin doses has documented structural damage. Two limits on that answer: nearly all of this work involves single or double doses in screened participants under supervision, and people with a personal or family history of psychosis are typically excluded from these trials, so the evidence says little about them.

Why does psilocybin help with mental illness?

Current evidence points to two connected mechanisms, neither fully established. First, psilocybin temporarily increases brain entropy and desynchronizes networks, disrupting the rigid, low-variety activity patterns associated with depression, OCD, and addiction. Second, the REBUS model proposes that this relaxes the precision of pathological beliefs, opening a window for revision. Zeifman et al. (2025) found 25 mg psilocybin decreased confidence in negative self-beliefs acutely and at four weeks, with the change correlating with session entropy and with subsequent well-being gains — the closest thing to an end-to-end test so far, in 11 healthy volunteers.

Sources & References

1. 1RTHM-00579·Carhart-Harris, Robin L et al. (2014). “The entropic brain: a theory of conscious states informed by neuroimaging research with psychedelic drugs..” Frontiers in human neuroscience.Study breakdown →PubMed →↩
2. 2RTHM-00943·Carhart-Harris, Robin L (2018). “The entropic brain - revisited..” Neuropharmacology.Study breakdown →PubMed →↩
3. 3RTHM-00489·Schartner, Michael M et al. (2017). “Increased spontaneous MEG signal diversity for psychoactive doses of ketamine, LSD and psilocybin..” Scientific reports.Study breakdown →PubMed →↩
4. 4RTHM-00463·Carhart-Harris, Robin L et al. (2017). “Psilocybin for treatment-resistant depression: fMRI-measured brain mechanisms..” Scientific reports.Study breakdown →PubMed →↩
5. 5RTHM-01038·Carhart-Harris, R L et al. (2019). “REBUS and the Anarchic Brain: Toward a Unified Model of the Brain Action of Psychedelics..” Pharmacological reviews.Study breakdown →PubMed →↩
6. 6RTHM-00752·Daws, Richard E et al. (2022). “Increased global integration in the brain after psilocybin therapy for depression..” Nature medicine.Study breakdown →PubMed →↩
7. 7RTHM-00911·Siegel, Joshua S et al. (2024). “Psilocybin desynchronizes the human brain..” Nature.Study breakdown →PubMed →↩
8. 8RTHM-02216·Zeifman, Richard J et al. (2025). “From relaxed beliefs under psychedelics (REBUS) to revised beliefs after psychedelics (REBAS)..” Scientific reports.Study breakdown →PubMed →↩