Structural brain changes seen after single magic mushroom psychedelic dose, study reports
Psilocybin may alter brain anatomy, research suggests. A single dose of the active compound in magic mushrooms has been found to induce structural changes in the brain that remain detectable a month later, according to a study of healthy volunteers who took the drug for the first time. The preliminary findings, if confirmed, could help explain the therapeutic potential of psychedelics for conditions such as anxiety, depression and addiction.
Nerve tracts become denser and more robust
The evidence for these anatomical changes came from specialised brain scans known as diffusion tensor imaging (DTI), which measure the diffusion of water molecules along the brain’s nerve bundles, or white matter tracts. DTI provides a window into the structural integrity and organisation of these pathways, and is sensitive enough to detect microstructural alterations even when conventional MRI scans appear normal. In this study, the scans revealed that a month after taking psilocybin, water diffusion had decreased along nerve tracts running from the front to the middle of the brain. The scientists interpreted this as suggesting that some nerve tracts had become denser and more robust – the opposite of what is typically seen in ageing and dementia, where tracts become more diffuse.
The exact biological mechanism behind the observed changes remains unclear. The drop in diffusion could be caused by the pruning of some nerve fibres or by the growth of new nerves that have not yet acquired their insulating sheaths, though further research is needed to establish which process is at work. One study noted that these changes may involve decreased axial diffusivity in prefrontal-subcortical tracts, a measure that correlates with reduced brain network modularity. “It’s remarkable to see potential anatomical brain changes one month after a single dose of any drug,” said Professor Robin Carhart-Harris, a neurologist at the University of California, San Francisco, and senior author of the study. “We don’t yet know what these changes mean, but we do note that overall, people showed positive psychological changes in this study, including improved wellbeing and mental flexibility.”
Therapeutic potential and the entropic brain effect
The researchers have long been exploring the “entropic brain effect”, a hypothesis that proposes psychedelics increase the diversity and unpredictability of neural activity, allowing the brain to break free from rigid, destructive cognitive patterns. In this study, electroencephalography (EEG) recordings taken within an hour of the 25mg psilocybin dose showed a surge in brain entropy, suggesting the brain was processing a greater variety of information than usual. Crucially, those participants who experienced the largest spike in entropy were also the most likely to report deeper psychological insight and improved wellbeing a month later – a correlation that underscores the link between flexible thinking and improved mental health.
“It suggests a psychobiological therapeutic action for psilocybin,” said Carhart-Harris. The idea is that by boosting cognitive flexibility, the compound may help people escape the entrenched thought patterns that underpin anxiety, depression and addiction. Professor Alex Kwan, a neuroscientist at Cornell University in New York, noted that studies in mice have shown psychedelics can rewire connections between nerves – a form of neuroplasticity. “The big question is whether the same occurs in humans,” he said. “This study comes closer than most to addressing that question, by giving evidence of lasting changes in brain structure after psychedelic use.” However, he cautioned that the study involved a small number of people and that DTI provides an indirect and limited view of brain connections.
How the study was conducted
The research, published in Nature Communications, involved 28 healthy volunteers who had never taken a psychedelic drug before. They took part in two sessions. In the first, they received a 1mg dose of psilocybin – so small it was considered a placebo. The scientists used EEG to measure their brain activity via electrodes on the scalp. Over the following weeks, participants completed a battery of tests to assess their wellbeing, depth of psychological insight and cognitive flexibility, while functional MRI scans and DTI monitored their brains.
A month after the placebo session, the same volunteers took a single 25mg dose of psilocybin, enough to produce a powerful psychedelic experience. During the trip and for weeks afterwards, the scientists repeated the same tests and brain monitoring. Within an hour, EEG revealed the surge in brain entropy. At the one-month mark, the DTI scans detected the drop in water diffusion along the front-to-middle nerve tracts – the anatomical change that the researchers described as “remarkable”.
The study was led by Carhart-Harris and colleagues, many of whom were formerly based at Imperial College London, a key centre for psychedelic research. Imperial is now conducting further studies exploring psilocybin for opioid use disorder, self-harm in young people and in couples therapy. Meanwhile, in the UK, psilocybin is currently classified as a Schedule 1 substance, requiring a Home Office licence for research. In July 2025, the UK government agreed in principle to recommendations that would exempt research institutions and approved clinical trials from that licence requirement, operating instead under less stringent Schedule 2 controls, though import and export rules remain unchanged and pharmaceutical industry requirements have not been altered.
