A single use of psilocybin can induce changes in brain activity that persist for several weeks. The deeper self-awareness that often follows such an experience is associated with long-term improvements in well-being.

The Effects of Psilocybin on the Brain

Studies conducted at the University of California, San Francisco, and Imperial College London have shown that a single dose of psilocybin—a psychoactive compound found in so-called "magic mushrooms"—can trigger physical changes in the brain that remain noticeable for up to a month. The research involved healthy adults with no prior experience with psychedelics. Although these participants did not have any mental health disorders, the findings may help explain psilocybin’s therapeutic potential for treating depression, anxiety, and addiction.

The researchers focused on the temporary increase in brain "entropy"—the diversity and unpredictability of neural activity. The results indicated that more varied brain activity may facilitate psychological insights, and that the psychedelic experience itself plays a crucial role in the long-term effects of psilocybin. A greater increase in entropy during the minutes and hours after taking a high dose was linked to stronger emotional insights the following day. Participants who reported significant insights were also more likely to experience improved well-being a month later.

Research Methods

Various methods were used to study brain activity, connectivity, and structure. Measurements were taken before psilocybin administration, during the experience, and one month afterward. Because the 28 volunteers had no psychiatric disorders, researchers were able to conduct a broader range of tests than is typically possible in clinical groups.

In the first phase of the experiment, participants received 1 mg of psilocybin, considered a placebo dose. Brain activity was monitored using electroencephalography (EEG). In the following weeks, psychological insight, well-being, and cognitive abilities were assessed. Functional MRI (fMRI) was also used to study brain activity, and diffusion tensor imaging (DTI) analyzed connections between different brain regions.

A month after the placebo, participants were given a 25 mg dose of psilocybin, sufficient to induce a pronounced psychedelic experience. During the trip, brain activity was again recorded with EEG, and the same psychological and visualization tests were repeated over the following weeks. This design allowed researchers to compare the effects of a full psychedelic dose with the results after the 1 mg placebo.

Changes in Brain Entropy

Within 60 minutes of taking 25 mg of psilocybin, EEG recorded an increase in brain entropy, indicating the generation and processing of a broader range of information under the influence of the substance. One month after the dose, DTI scans revealed that neural tracts had become denser and more integrated. This pattern is the opposite of changes typically associated with aging, where neural tracts become more diffuse.

The researchers note that further studies are needed to fully understand these structural changes, but consider this result a previously unobserved sign that psychedelics can induce lasting changes in the brain.

Long-Term Effects on Insight and Well-Being

The day after taking 25 mg of psilocybin, 27 out of 28 participants described the experience as the most unusual state of consciousness in their lives. The remaining participant ranked it among their top five most unusual experiences. Participants also reported significantly greater psychological insight after the 25 mg dose compared to the 1 mg placebo.

Well-being scores improved two and four weeks after the high dose. Assessments included responses to statements such as "I feel optimistic about the future" and "I handle problems well." A month after the experiment, participants also performed better on tests of cognitive flexibility—the ability to adapt thinking and respond to changing information.

The Link Between Insight, Entropy, and Well-Being

Participants who experienced the greatest increase in brain entropy in the initial minutes and hours after taking psilocybin were more likely to report significant insights the next day. These insights, in turn, were associated with greater improvements in well-being a month later. The researchers concluded that psychological insight is a key factor in subsequent improvements in well-being.

The data obtained may help doctors more precisely tailor psilocybin doses for patients with mental health disorders—for example, to induce a sufficient level of brain entropy for meaningful insight, while avoiding an overly intense experience.

Future Prospects

The study’s results expand our understanding of the mechanisms of psilocybin’s action and its potential benefits for treating mental health conditions. It has been established that the psychedelic experience and the associated changes in brain activity are key components of how psychedelic therapy works.