Meditation -- which is widely believed to be an antidote to mental health issues -- may not always be a pleasant experience for everyone, according to scientists who advocate more research into such practices.
The research, led by scientists from University College London (UCL) in the UK, found that over a quarter of people who regularly meditate have had a 'particularly unpleasant' psychological experience related to the practice, including feelings of fear and distorted emotions.
Published in the journal PLOS ONE, the study also found those who had attended a meditation retreat, those who only practiced deconstructive types of meditation, such as Vipassana (insight) and Koan practice (used in Zen Buddhism), and those with higher levels of repetitive negative thinking, were more likely to report a 'particularly unpleasant' meditation-related experience.
However, the study, which comprised an international online survey of 1,232 people who had at least two months' meditation experience, found female participants and those with a religious belief were less likely to have had a negative experience.
"These findings point to the importance of widening the public and scientific understanding of meditation beyond that of a health-promoting technique," said Marco Schlosser, a researcher at UCL.
"Very little is known about why, when, and how such meditation-related difficulties can occur: more research is now needed to understand the nature of these experiences," Schlosser said in a statement.
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"When are unpleasant experiences important elements of meditative development, and when are they merely negative effects to be avoided?" he said.
The study, conducted with researchers at Witten/Herdecke University in Germany, and the University of Ljubljana in Slovenia, was triggered by a limited but growing number of research reports and case studies, which indicate psychologically unpleasant experiences can occur during meditative practice.
Some traditional Buddhist texts also reference vivid accounts of similar experiences. However, very little is known about the prevalence of these experiences.
Of the 1,232 participants, 25.6 per cent indicated that they had previously encountered particularly unpleasant meditation-related experiences.
More male participants, 28.5 per cent, experienced a particularly unpleasant experience, compared to 23 per cent of female participants.
About 30.6 per cent of those who did not have a religious belief had a particularly unpleasant experience, compared to 22 per cent of those who had a religious belief.
More people, 29.2 per cent, who practised only deconstructive types of meditation reported a particularly unpleasant experience, compared to 20.3 per cent who only engaged in other meditation types.
About 29 per cent of those who had been on a meditation retreat (at any point in life) had a particularly unpleasant experience, compared with 19.6 per cent, who had never been on a retreat.
"Most research on meditation has focussed on its benefits, however, the range of meditative experiences studied by scientists needs to be expanded. It is important at this point not to draw premature conclusions about the potential negative effects of meditation," Schlosser said.
Researchers acknowledged a number of limitations in the study.
The study only asked one question to capture prevalence of particularly unpleasant meditation-related experiences. The data does not provide any indication of the exact type of experiences or their severity and impact.
The study did not assess possible pre-existing mental health problems, which could have confounded the prevalence estimate of particularly unpleasant meditation-related experiences.
The data also does not allow researchers to clearly infer whether meditation caused these experiences.