Scientists have made a remarkable discovery: a single dose of psilocybin — the active compound in magic mushrooms — can cause measurable physical changes in the human brain that persist for up to a month. As reported by The Guardian, the findings were published on 5 May 2026 in the peer-reviewed journal Nature Communications, and represent one of the most significant pieces of evidence yet that psilocybin does more than temporarily alter perception — it may actually reshape the brain.
What Did the Study Find?
The research was led by scientists at the University of California, San Francisco (UCSF) and Imperial College London. It involved 28 healthy adults with an average age of 41, none of whom had ever taken a psychedelic substance before.
Participants first took a 1mg dose of psilocybin — small enough to function as a placebo — and were monitored over several weeks. A month later, they took a full 25mg dose, enough to trigger a powerful psychedelic experience. Researchers then used EEG brain activity scans and specialist MRI imaging to track what happened in the brain from one hour after the dose all the way through to one month later.
The results were striking. Specialised MRI scans taken one month after the high dose revealed structural changes in areas connecting the front to the middle of the brain — suggesting a single dose had produced an enduring impact on brain anatomy.
What Is Brain Entropy — and Why Does It Matter?
One of the study’s key findings centres on a concept called brain entropy — the diversity and complexity of neural activity occurring in the brain at any one time. Higher entropy means the brain is generating a wider range of activity patterns, rather than staying locked into rigid, repetitive loops.
Within one hour of taking the 25mg dose, EEG scans showed a significant surge in brain entropy. Crucially, the degree of that entropy during the experience predicted how much psychological insight participants reported feeling the following day — and that insight, in turn, predicted improvements in their wellbeing and mental flexibility weeks later.
In other words, the intensity of the psychedelic experience itself appears to be an important part of why psilocybin has therapeutic effects — not just a side effect to be managed.
Less Rigid, More Connected
Beyond entropy, the study also found that the brain became less rigid and more interconnected over time following the high dose. Researchers observed a decrease in what is called “network modularity” — meaning the brain’s networks, which normally operate in relatively separate clusters, began communicating more freely with one another.
This pattern of decreased rigidity and increased connectivity has also been observed in depression research, where it is associated with better mental health outcomes. Participants in the study showed improvements in cognitive flexibility, psychological insight and overall wellbeing one month after their single dose.
What Do the Researchers Say?
Prof Robin Carhart-Harris, senior author on the study and a neurologist at UCSF, told The Guardian: “It’s remarkable to see potential anatomical brain changes one month after a single dose of any drug. 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.”
The researchers are careful not to overclaim. The study was conducted on healthy volunteers, not people with depression or anxiety, so direct clinical conclusions cannot yet be drawn. But the findings may help explain why psilocybin has shown consistent promise in therapeutic settings — and why its effects can outlast the experience itself by weeks or months.
Why This Matters for Psilocybin Research
Until now, much of the science around psilocybin has focused on how it changes brain function — the patterns of activity and communication between regions. This study goes a step further, suggesting the drug may also change brain structure: the physical architecture of neural connections.
If confirmed in larger trials, this would be a significant development. It raises the possibility that psilocybin is not simply producing a temporary shift in mood or perception, but is actively promoting neuroplasticity — the brain’s ability to reorganise and form new connections.
This lines up with a growing body of evidence suggesting psilocybin could have therapeutic applications for depression, anxiety, addiction and PTSD. The debate around whether treatments like this should be made available through health services such as the NHS is already well underway — and studies like this will only add to the pressure on regulators to act.
Frequently Asked Questions
Can a single dose of psilocybin really change the brain?
According to a May 2026 study published in Nature Communications by researchers at UCSF and Imperial College London, yes. Specialised MRI scans found structural changes in areas of the brain one month after participants took a single 25mg dose of psilocybin.
How long do psilocybin’s effects on the brain last?
The study found that measurable anatomical brain changes were still detectable one month after a single dose. Improvements in wellbeing, cognitive flexibility and psychological insight were also reported at the one-month mark.
What is brain entropy and how does psilocybin affect it?
Brain entropy refers to the diversity of neural activity in the brain. Psilocybin was found to significantly increase entropy within one hour of a high dose, putting the brain into a more complex, flexible state. Higher entropy during the experience predicted greater insight and better mental health outcomes weeks later.
Was this study done on people with depression?
No. The 2026 UCSF study was conducted on 28 healthy adults with no prior psychedelic experience. While the findings are relevant to conditions like depression and anxiety, direct clinical conclusions require further trials in patient populations.
Is psilocybin legal in the UK?
Psilocybin remains a Class A, Schedule 1 controlled substance in the UK. It is currently only permitted for use in authorised clinical research under strict medical licences. It is not available as a prescription treatment.
Source: The Guardian / Nature Communications, UCSF & Imperial College London, May 2026. Thanks for reading.
