Hallucinations and delusions in the general population are more common than previously thought.
An international study led by The University of Queensland and Harvard Medical School found that hearing voices and seeing things others cannot impacts about five per cent of the general population at some point in their lives.
Queensland Brain Institute researcher Professor John McGrath said the study, involving more than 31,000 people from 19 countries, was the most comprehensive ever completed.
"We used to think that only people with psychosis heard voices or had delusions, but now we know that otherwise healthy, high-functioning people also report these experiences," Professor McGrath said.
"Of those who have these experiences, a third only have them once and another third only have two-to-five episodes across their life. These people seem to function reasonably well.
"So it's incredibly interesting that not only is hearing voices more common than previously thought, but it's not always linked to serious mental illness."
The study was a population-based survey which involved approaching randomly selected members of the community, sitting down with them and conducting a very detailed interview about their mental health.
"These people were representative of the general population, not seeking mental health assistance," Professor McGrath said.
The study found that auditory hallucinations are more common in women than men, and they are also more common in people from wealthier countries.
Professor McGrath said the findings could help generate new research into the causes of these isolated symptoms.
"In particular, we are interested in learning why some people recover, while others may progress to more serious disorders such as schizophrenia," he said.
"We need to understand why it's temporary for some people and permanent for others. We can use these findings to start identifying whether the mechanisms causing these hallucinations are the same or different in both situations.
"We need to rethink the link between hearing voices and mental health - it's more subtle than previously thought.
"While people may experience a false perception such as mistakenly hearing their name called out in public, hallucinations and delusions are quite detailed, for example hearing voices that no one else can hear or a belief that somebody else has taken over your mind.
"People should be reassured that there isn't anything necessarily wrong with them if it happens once or twice, but if people are having regular experiences, we recommend that they seek help."
The study was published in JAMA Psychiatry, and funded by a National Health and Medical Research Council John Cade Fellowship.