Being involved in sibling bullying triples the risk of psychotic disorders in adulthood, new research finds.
The risk is tripled whether the person is the victim or the bully.
A child who is bullied at home and at school has four times the chance of developing a psychotic disorder later on.
Psychotic disorders, like schizophrenia, are those that involve becoming detached from reality.
This could include experiencing hallucinations, delusions or paranoid thoughts.
Professor Dieter Wolke, study co-author, said:
Bullying by siblings has been until recently widely ignored as a trauma that may lead to serious mental health problems such as psychotic disorder.
Children spend substantial time with their siblings in the confinement of their family home and if bullied and excluded, this can lead to social defeat and self-blame and serious mental health disorder - as shown here for the first time.
The results come from a study of 3,600 children who were followed over six years.
Of these, 664 children were victims of sibling bullying, 486 pure bullies and 771 were both bullies and victims.
The results showed that the more frequently they were involved in sibling bullying, the higher the chance they would develop a psychotic mental health problem.
Those who reported being involved in sibling bullying - as either bully or victim - had two to three times the risk of developing a psychotic disorder later on.
Slava Dantchev, the study's first author, said:
*If the bullying occurs at home and at school the risk for psychotic disorder is even higher. These adolescents have no safe place.
Although we controlled for many pre-existing mental health and social factors, it cannot be excluded that the social relationship problems may be early signs of developing serious mental health problems rather than their cause.*
The study was published in the journal Psychological Medicine (Dantchev et al., 2018).