A Single Dose of Psilocybin Linked to Lasting Anatomical Brain Changes
A single psilocybin dose may induce lasting changes in brain structure and flexibility.
While many medications require daily use to stay effective, a single psychedelic trip may be enough to trigger biological changes that last for weeks.
A new study from the University of California, San Francisco (UCSF) and Imperial College London shows that psilocybin can physically remodel brain structure and improve mental flexibility after just one session.
The findings suggest that the experience itself is a catalyst for lasting brain health.
The long-term impact of psilocybin on the brain
Modern medicine is currently seeing a psychedelic renaissance, with one drug in particular sitting in the spotlight. Psilocybin, the active compound in magic mushrooms, has shown promise in treating conditions such as depression, anxiety, and addiction.
Unlike conventional antidepressants, which often require daily doses and weeks or months to take effect, psilocybin may offer a much faster alternative.
While scientists know that these drugs drastically alter brain function during a trip, it has been unclear whether a single dose can cause lasting anatomical and functional changes in the human brain.
The researchers of the new study aimed to determine if psilocybin’s therapeutic effects are rooted in physical brain changes, using healthy, first-time users to establish a clear baseline of the drug’s biological impact. This approach allowed the team to see how the drug affects the brain without the noise of pre-existing mental health conditions.
Tracking how psilocybin changes brain structure and connectivity
The team recruited 28 healthy volunteers who were entirely new to psychedelics. Participants first received a 1 mg dose as a placebo; they were then given a high 25 mg dose of psilocybin to induce a full psychedelic experience, one month later.
The researchers used several imaging tools to track the results, including an electroencephalogram (EEG) to monitor electrical activity during the trip and magnetic resonance imaging scans to study brain connectivity and structure.
Within 60 minutes of taking the high dose, the EEGs showed a spike in brain entropy.
Brain entropy
Brain entropy refers to the diversity and complexity of neural activity; a high entropy state means the brain is processing a richer, less predictable range of information, moving away from rigid, repetitive patterns.
These changes were not temporary, and one month later, participants also reported higher levels of well-being and cognitive flexibility.
“Psilocybin seems to loosen up stereotyped patterns of brain activity and give people the ability to revise entrenched patterns of thought,” said first author Dr. Taylor Lyons, a research associate at Imperial College London. “The fact that these changes track with insight and improved well‑being is especially exciting.”
One month after the high dose, the brain's neural tracts were also denser and showed more integrity—the functional opposite of what happens as the brain ages.
Neural tracts
Neural tracts are bundles of fibers that connect different regions of the brain, allowing information and electrical signals to travel from one area to another.
The degree of brain entropy during the trip predicted how much insight the person felt the next day, which then predicted their improved well-being a month later.
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Future clinical implications of psilocybin therapy
The study suggests that the psychedelic experience itself is an important part of the therapy, rather than just being a side effect of the drug's chemistry.
“Psychedelic means ‘psyche-revealing,’ or making the psyche visible,” said senior author Dr. Robin Carhart-Harris, a professor of neurology at UCSF. “Our data shows that such experiences of psychological insight relate to an entropic quality of brain activity and how both are involved in causing subsequent improvements in mental health. It suggests that the trip—and its correlates in the brain—is a key component of how psychedelic therapy works.”
In the future, clinicians might personalize psilocybin doses to ensure a patient reaches the specific level of brain entropy needed to trigger a psychological breakthrough.
However, there are limitations to consider. The study was exploratory and used a small group of 28 people. Since the participants were healthy, it cannot be certain that the results will be identical in clinical populations.
It is also unknown if these anatomical changes are permanent or if patients might eventually need top-up doses.
Despite these questions, the study shows that by temporarily loosening the brain’s rigid patterns, psilocybin creates a window for people to revise their lives.
“We already knew psilocybin could be helpful for treating mental illness. But now we have a much better understanding of how,” said Carhart-Harris.
Reference: Lyons T, Spriggs M, Kerkelä L, et al. Human brain changes after first psilocybin use. Nat Comm. 2026. doi: 10.1038/s41467-026-71962-3
This article is a rework of a press release issued by the University of California, San Francisco. Material has been edited for length and content.
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