Children who experience hallucinations may be at a five-fold risk of suicidal behaviour, a large international study has found.

Hallucinations among otherwise healthy people are more common than first thought and have been linked to a significant increased risk of self-harm, a large international study has found.

Research involving 33,000 people from 19 countries found one in 20 people had experienced a hallucination at some point in their lives, after excluding those with serious mental illness.

Professor John McGrath at the University of Queensland's Brain Institute - who was part of the study - says they also found a psychotic experience was associated with a two-fold risk of suicidal thoughts and behaviour.

This risk was even greater for those who had experienced a visual or auditory hallucination during childhood, Prof McGrath said.

"The risk of suicidal thoughts was five or six times higher in children under 12 who had experienced psychosis," Prof McGrath said.

A psychotic experience appears to be caused by general psychological distress. For children, it is often associated with severe trauma such as sexual abuse.

Contrary to popular belief it is "wrong" to believe that such an experience is always a sign of a future schizophrenia diagnosis, says Prof McGrath.

"Feeling depressed or anxious is part of life and there are some people who will occasionally will have an auditory hallucination as part of that general distress; we did not know that until quite recently and now we see that quite clearly," Prof McGrath told AAP.

"We are now trying to work out the 'so what' of these experiences," he said.

There has been a growing body of evidence linking psychotic episodes to suicidal thoughts and behaviours, say researchers.

Despite this, it has remained unclear if the presence of mental illness explained the association or it was entirely unique.

To investigate this further a team of international researchers examined the links between psychotic experiences and suicide risk within the general population.

The study, published in JAMA Psychiatry and funded by the National Health and Medical Research Council, involved more than 33,000 people in 19 countries who were randomly selected.

Participants were asked about psychotic experiences, mental disorders, as well as any suicidal thoughts, plans and attempts through the WHO World Mental Health (WMH) Surveys.

The study found psychotic experiences, such as hearing voices, were independently linked to an increased risk of self-harm.

"Psychotic experiences are associated with elevated odds of subsequent SBTs (suicidal thoughts and behaviours) across the life -course that cannot be explained by antecedent mental disorders," the authors wrote.

While more research is needed, Prof McGrath believes the findings could have important implications for the way doctors screen patients for suicide risk.

"We did not realise how common these experiences were and now we've linked them to increased risk of self-harm," he told AAP.

"Our study suggests asking patients if they've heard voices or have 'strange' beliefs may provide more information to suggest they need monitoring, particularly in young people."

Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14.

Suicide Call Back Service 1300 659 467.

MensLine Australia 1300 78 99 78.

Multicultural Mental Health Australia www.mmha.org.au.

Local Aboriginal Medical Service details available from www.bettertoknow.org.au/AMS