Psilocybin Induces Anatomical and Functional Brain Changes in Study

A study by scientists at UC San Francisco and Imperial College London reports that a single dose of psilocybin produces measurable changes in brain activity and structure that can persist for up to a month. Conducted in healthy volunteers with no prior psychedelic use, the research links these effects to shifts in brain “entropy,” or the diversity of neural activity, and to longer-term improvements in well-being.

The findings, published in Nature Communications, indicate that a high dose of psilocybin increases brain entropy within minutes to hours after administration. This heightened state reflects a broader range of neural activity. The degree of entropy observed during this period was associated with how much psychological insight participants reported the following day. Those who experienced greater insight were also more likely to report improved well-being weeks later. 

Senior author Robin Carhart-Harris explained: "Psychedelic means ‘psyche-revealing,’ or making the psyche visible. 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.”

The study included 28 participants and compared the effects of a low 1 mg dose, treated as a placebo, with a 25 mg dose capable of producing a strong psychedelic experience. Researchers used electroencephalography (EEG) to measure brain activity during the sessions and followed up with functional MRI and diffusion tensor imaging to assess brain function and connectivity over time.

Within an hour of the higher dose, EEG data showed increased entropy, suggesting more complex brain activity. One month later, diffusion tensor imaging revealed that neural tracts appeared denser and showed greater integrity, which contrasts with patterns typically seen in aging. The researchers noted that further work is needed to interpret these structural changes.

Participants reported higher levels of psychological insight after the 25 mg dose compared to the placebo. Nearly all described the experience as among the most unusual states of consciousness they had encountered. In the weeks following the session, they also reported improved well-being and demonstrated better cognitive flexibility.

Taylor Lyons, first author of the study, said: "Psilocybin seems to loosen up stereotyped patterns of brain activity and give people the ability to revise entrenched patterns of thought. The fact that these changes track with insight and improved well‑being is especially exciting.”