Scientists gave people a “heroic” dose of psilocybin and then looked at their brain. Here’s what happened

By Jackie Flynn Mogensen edited by Claire Cameron

A psychedelic trip—on “magic mushrooms,” to be precise—may cause physical changes to the brain, a new imaging study finds. The results could one day help explain why people who take psilocybin—a psychoactive ingredient in such mushrooms—can feel a multitude of effects, from bliss and euphoria to anxiety, discomfort and hallucinations, as well as long-term effects of the drug.

“No one has ever properly tested whether and how the brain changes when someone takes psychedelics for the first time,” says Robin Carhart-Harris, a professor of neurology at the University of California, San Francisco. Users often describe the first time taking magic mushrooms as a significant experience, he says. But understanding what’s going on at the biological level has so far eluded scientists.

Now, in the new study, Carhart-Harris and his colleagues may have taken a step closer to answering that question. The team gave 28 healthy people who’d never tried a psychedelic 25 milligrams of psilocybin—the equivalent of a “heroic” dose of magic mushrooms, Carhart-Harris says—and looked at their brain using a variety of scanning techniques, including electroencephalography (EEG), magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI).

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The researchers scanned the brains of the participants brains before and after the dose using both MRI and DTI to track any possible changes to the organs’ activity and wiring, Carhart-Harris says. The team also monitored the participants’ brain using EEG during the trip and asked them about their well-being before and after they took the psilocybin.

After a single dose, the team detected changes in brain activity that correlated with well-being as much as a month after the participants took the drug. When participants’ brain activity was “richer” and less predictable (a measurement that Carhart-Harris and his team refer to as greater “entropy”), they tended to report having increased “psychological insight”—new ways of thinking about themselves, their problems, their past, and more—shortly after the trip.

“We know what’s going on in your brain when you’re under the influence—when you’re experiencing the ‘magic’—and we know what it will translate to soon after in terms of psychological insight,” Carhart-Harris says. Greater psychological insight also tracked with reports of higher mental well-being a month after the dose.

The team also found changes to the brain’s wiring. After taking psilocybin, “tracts” in the brain that run from the prefrontal cortex to the middle of the organ appeared to be “less diffuse” along their length, meaning they could have become more compact or thinner, Carhart-Harris says. Whether that alteration is beneficial or not is unclear.

The study is “exciting,” says Alan Davis, director of the Center for Psychedelic Drug Research and Education at the Ohio State University, who was not involved in the new research. “Importantly, it demonstrates the importance of acute and enduring psychological insights or realizations in predicting outcomes of psilocybin experiences.” And the research provides some “clarity” on the mechanisms of how psychedelics may eventually help patients with mental health challenges, he says.

The findings are preliminary and perhaps raise more questions than they answer. For instance, how long do these brain changes last? The study only followed people for a month. And while the participants’ well-being outcomes may have been positive, it’s not clear whether any noted changes to the brain may have unexpected or even negative effects down the line. A recent policy shift at the federal level could help expedite this work. In April President Donald Trump signed an executive order aimed at expanding research on psychedelics. That effort could help answer some of the big questions in the field, Carhart-Harris says, including the enduring or long-term effects of psychedelics on neurobiology. His research team plans to explore using psilocybin to treat conditions such as chronic pain disorders, anorexia nervosa, and more to try to tease out more answers about how the drug changes the brain.

“The honest answer is: we don’t know [how psilocybin changes the brain]. We don’t have enough information,” Carhart-Harris says. There’s “a lot to do” to understand “some major questions in this space.”

The findings were published on Tuesday in the journal Nature Communications.