Bullying can literally drive young children insane, researchers have revealed.
Being bullied increased the risk of psychotic symptoms by the age of adolescence up to four times, a study found.
Children's symptoms included hallucinations, paranoid delusions such as believing they are being spied on, and irrational thoughts.
Psychologists followed 6,437 children from birth to 13 years. The children took part in annual face-to-face interviews, as well as psychological and physical tests. Parents were also asked to complete questionnaires about their sons' and daughters' development.
At the age of 13, the children were interviewed about their experiences of psychotic symptoms in the previous six months.
The researchers found children who suffered physical or emotional bullying were twice as likely to develop psychotic symptoms by early adolescence as children who were not bullied.
However, if they experienced sustained bullying over a number of years they could be four times more at risk.
Study leader Professor Dieter Wolke, from the University of Warwick, said: "Our research shows that being victimised can have serious effects on altering perception of the world, such as hallucinations, delusions or bizarre thoughts where the person's insight into why this is happening is reduced.
"This indicates that adverse social relationships with peers is a potent risk factor for developing psychotic symptoms in adolescence and may increase the risk of developing psychosis in adulthood."
The researchers used data from the Avon Longitudinal Study of Parents And Children (ALSPAC).
