A new study suggests that students who witness their peers being abused verbally or physically are likely to suffer from metal stress themselves.
The study, covering nearly 2,000 students in the ages of 12 to 16 from 14 British public schools, also found that bullies and bystanders are also more susceptible to take drugs and alcohol.
Lead author Ian Rivers said: "It's well documented that children and adolescents who are exposed to violence within their families or outside of school are at a greater risk for mental health problems than those children who are not exposed to any violence.
"It should not be a surprise that violence at school will pose the same kind of risk."
Students were given a list of bullying behaviours, like name-calling, kicking, hitting, spreading rumours and threatening violence. Thereafter, they were asked if they had themselves bullied, seen bullying or been the victim of any of the types of behaviours pointed out to them, during the previous nine-week school term and how often.
Almost 63percent reported being witnesses to peers being bullied. About 34percent students said they had been bullied and 20percent admitted to being bullies. Girls reported witnessing more bullying than boys.
The students were also asked if they felt anxious, inferior and hostile and turned to drugs, tobacco or alcohol.
It was seen that students who had witnessed bullying were more vulnerable to greater psychological distress than the victims or the bullies.
Rivers said: "It is possible that those students who had been victimized at different times may be experiencing it all over again psychologically.
"Meanwhile, those who are witnesses may worry that they, too, will be the bully's target sometime in the future and that causes great distress and anxiety."
Rivers and co-author Paul Poteat of Boston College hope their work will increase the awareness of schools about the possible psychological effect of witnessing bullying on their students.
Rivers added: "School psychologists can help students realize that they don't have to be a bystander. They can be a defender."
The findings of the study have appeared in the December issue of School Psychology Quarterly, published by the American Psychological Association.