Teenagers who had a classmate die by suicide are significantly more likely to think about or attempt suicide themselves over the following two years, according to a new study.

The idea that being exposed to a suicide can spur suicidal thoughts or actions is not a new one; it’s called "suicide contagion." But until now, researchers didn’t have evidence that it affected Canadian teens.

For this new study, published in the Canadian Medical Association Journal, researchers looked at Statistics Canada data on more than 22,000 teens aged 12–17 years from across the country.

They found that the suicide of a schoolmate increased the risk of “suicidality” – meaning suicidal thoughts or actions -- regardless of whether the young person personally knew the teen who had died.

This risk was particularly strong among 12 to 13 year olds; they were five times more likely to have suicidal thoughts after exposure to a schoolmate's suicide than those who had had no exposure.

In all, they found that 15 per cent youth of this age thought about suicide after a schoolmate had died of suicide, versus 3 per cent of youth who had not been exposed to suicide.

As well, in this age group, 7.5 per cent actually attempted suicide after a schoolmate's suicide, compared with only 1.7 per cent of youth with no exposure.

The "suicide contagion" effect was less pronounced in older teens, although 14 to 15 year olds exposed to suicide were still almost three times more likely to have suicidal thoughts, and 16 to 17 year olds were twice as likely.

The study also found that as teens age, they are more likely to be exposed to suicide: by 16–17 years, 24 per cent of teens had a schoolmate die by suicide, while 20 personally knew someone who died by suicide.

Senior author Ian Colman, who is a researcher in mental health epidemiology at the University of Ottawa, says it's clear from this study that the suicide contagion effect appears to be real, but  the question is how might suicde be contagious? It’s possible, he says, that the suicide of a classmate has an effect on teens -- especially younger ones -- because it exposes them to an idea they never considered before.

“For vulnerable kids, this might be the first time that they think that suicide might be a solution to their problems,” he told CTV News. “And that is really dangerous, especially if that suicide is portrayed in a very romantic fashion and there is a massive outpouring of love from the community. Then for those vulnerable youth, they might see suicide... as an attractive solution."

The researchers say the findings suggest that suicide prevention strategies should target all the schoolmates of a teen who has died of suicide, not just the teen’s close friends.

“This can be a big public health problem when one student dies at a very large school, then there could be thousands of students who are affected by that, and we need to think about what we can do to help those children and make sure they are getting help for their problems as well," Colman said.

In a related commentary, Dr. India Bohanna, of the School of Public Health at James Cook University in Australia says this study "provides convincing evidence that, among young people, exposure to suicide is a risk factor for future suicidal behaviour.

"The idea that suicide is contagious has always been controversial for various reasons; however, this important study should put many, if not all, doubts to rest,” she writes.

She says a concerted effort needs to be made toward developing effective suicide prevention strategies.

“We need to know what works in mitigating the risk of contagion and why,” she said.

With a report from CTV medical specialist Avis Favaro and producer Elizabeth St. Philip