Irish teenagers who have concerns about their sexual orientation have much higher levels of mental health problems and are much more likely to attempt suicide than their peers, a new study has found.

These teenagers are also significantly more likely to be victimised.

Researchers questioned over 1,100 Irish students attending 17 mixed-gender secondary schools. The average age of the participants was 14 and 55% were male. Some 5% of the students admitted to having concerns about their sexual orientation.

The study found that those with concerns had more mental health difficulties than their peers, including anxiety, depressive symptoms and behavioural problems. They were also significantly more likely to have attempted suicide - 29% versus 2% of their peers.

These students were also much more likely to have been physically assaulted than their peers - 40% versus 8%, and sexually assaulted - 16% versus 1%.

Substance misuse was also more common among them, with one in five admitting to drinking alcohol frequently compared to 1% of their peers. Three in four were also smokers compared with less than one in five of their peers.

These young people were also much more likely to have used marijuana - 41% versus 2% of their peers.

The study also noted that the vast majority of teenagers (90%) with concerns about their sexual orientation said they had already had sex, compared to just 4% of their peers.

According to the researchers, this study supports the view that young people become concerned about their sexual orientation from a young age. While previous studies suggest that lesbian, gay, bisexual or transgender (LGBT) young people often reveal their sexual orientation towards the end of secondary school, this appears to happen later among Irish LGBT people.

The period during which sexual orientation is hidden often coincides with feelings of vulnerability and distress.

"The current findings support the need for an environment that facilitates adolescents' free expression of their sexual orientation concerns," the researchers said.

They suggested that school and community-based health awareness programmes should include the topic of sexual orientation, with the aim of supporting young people with concerns and reducing stigma and victimisation.

They also added that awareness of the mental health issues these young people may face should become standard training for professionals working with them.

Details of these findings are published in the Irish Medical Journal.