Mindfulness—that buzzword that means, “focusing on emotions in the present moment”—can lead to false memories being implanted in the brain. A new study found that a session as short as 15 minutes could leave people less able to distinguish between words they had seen written down, and those they had thought about in their heads alone—casting doubt over whether this much lauded practice may cause more harm than good.

Researchers at the University of California, San Diego (UCSD), examined the disruptive properties of mindfulness, which teaches the quieting of the mind and learning to acknowledge and then dismiss negative thoughts, by putting 153 undergraduate students through a series of experiments designed to test the practice’s effects on their concept of reality and imagination.

Half of the participants were tasked with spending 15 minutes focusing on their breathing. The others were asked to think normally, before being asked to recall a list of 15 words, all of which related to garbage (refuge, sewage, waste, etc.). The list did not include the word trash.

But 39 percent of those tested falsely believed they had seen trash written down, compared to almost half that rate for those who had let their minds wander, with two further experiments exhibiting the same results.

“When memories of imagined and real experiences too closely resemble each other, people can have difficulty determining which is which, and this can lead to falsely remembering imagined experiences as actual experiences,” explained Brent Wilson, a psychology doctoral candidate at the University of California. “Our results highlight an unintended consequence of mindfulness meditation: memories may be less accurate,” he continued. “The same aspects of mindfulness that create countless benefits can also have the unintended negative consequence of increasing false-memory susceptibility.”

The study is among the first to suggest that mindfulness may have negative qualities. Health professionals and celebrities alike have been vocal proponents of the millennia-old practice since it came back in vogue two years ago, with Oprah Winfrey, Angelina Jolie, and Emma Watson among those touting its positive effects.

Prior research, too, has proved favorable, with a study from Oxford University showing that the effects of mindfulness-based cognitive therapy were akin to medication in stopping people from sinking back into depression. It has also been found to boost productivity, improve relationships and decrease anxiety, and serves as an antidote to a Harvard study which found that allowing the mind to wander—which mindfulness rallies against—makes people unhappy.

Given the reams of positive press mindfulness has long been associated with, some are skeptical of research critiquing its effects. “I don’t see how it could have any bearing on false memories,” says Peter Leigh, an entrepreneur who uses the technique. “We practice mindfulness so that we can experience life fully, in the now, rather than re-living the cycle of past experiences or conjuring false futures. Only by being in the now, can we act fully to pave the future.”

Mindfulness has become big business in the past few years, with an outpouring of apps and workshops on offer aimed at people hoping to retrain their thinking. Headspace, a popular app created by a former monk, is now worth some $386m. Major companies like Google have also adopted the practice, where courses are offered to employees.

But the study out of UCSD raises difficult questions, particularly given how widespread mindfulness has become. How, for example, might it affect those whose ability to remember is paramount? How might witnesses who practice mindfulness be affected on the stand? Might someone recall a false event after training his or her mind to think in this way?

The potential damage of misremembering is vast, and if mindfulness does give rise to such behaviors, perhaps we need a new way to meditate.