Psilocybin May Induce Lasting Physical Brain Changes, Study Finds

Neural Entropy and the Peak Experience

Psilocybin—the active compound in magic mushrooms—appears to trigger a distinct mechanism for therapeutic change. In a study of 28 volunteers who had never used psychedelics, a 25-mg dose prompted an immediate spike in brain entropy. This metric tracks the diversity and unpredictability of neural activity, a state of complexity that seems to underpin psychological breakthroughs.

“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,” said senior author Robin Carhart-Harris, PhD, the Ralph Metzner Distinguished Professor of Neurology at UCSF.

The intensity of this entropy predicted the emotional insight participants reported the following day. All but one participant described the session as the single most unusual state of consciousness they had ever experienced, with these insights linking directly to sustained well-being one month later.

Long-Term Structural Remodeling

The study went beyond transient activity, uncovering structural alterations that persisted long after the drug cleared the system. Using diffusion tensor imaging (DTI) to track water movement along neural pathways, the team identified increased density and integrity in neural tracts one month post-dose. Notably, this pattern is the reverse of typical aging, where tracts often become more diffuse.

Researchers also observed reductions in brain network modularity—the segregation of neural systems—which correlated with better well-being. Decreases in axial diffusivity within prefrontal-subcortical white matter tracts suggest underlying neuroplasticity.

Of an array of findings, decreases in the diffusivity of large tracts running between the prefrontal cortex and the center of the brain are perhaps the most intriguing, Carhart-Harris said. We don’t yet know what the functional implications of these changes are, but we do plan more research to find out.

Cognitive Gains and Methodological Limits

Participants underwent a controlled sequence: a 1-mg placebo dose followed by a 25-mg high dose. One month after the high-dose session, volunteers showed improved performance on tests of cognitive flexibility, suggesting a heightened capacity to adapt to new information.

Psilocybin seems to loosen up stereotyped patterns of brain activity and give people the ability to revise entrenched patterns of thought, said lead author Taylor Lyons, PhD, a research associate at Imperial College London. The fact that these changes track with insight and improved well-being is especially exciting.

The investigators cautioned that the study was exploratory, involving a small sample of healthy volunteers rather than psychiatric patients. Furthermore, because the study utilized a fixed-order design, they noted that practice or expectation effects cannot be fully ruled out. The team emphasized that further research is required to replicate these findings and clarify their clinical significance.