One-third of 17 and 18-year-olds in Ireland have had sex, however one in 10 of these has never used a condom and at least one in seven felt pressured into having sex, new research has found.

According to the findings, 33% of Ireland's 17 and 18-year-olds have had sexual intercourse, while 40% have had oral sex.

Among those who have had sex, 56% said they always used a condom, however 11% admitted that they had never used one. Meanwhile, 79% said they or their partner had used some form of contraception, however 6% said they had hardly ever or never used any form of contraception.

Some 13% of 17 and 18-year-olds who have had sex admitted that they felt a little pressure to do so, while 4% said they felt a lot of pressure. Some 6% said they were afraid of losing their partner if they did not have sex with them.

The findings are based on the latest research from the Growing Up in Ireland study, an ongoing study of young people in Ireland. This research was based on interviews with over 6,000 17 and 18-year-olds, who have been participating in the study since 2007, when they were nine years old.

It found that when it comes to health and weight, most were in good health, however 20% were found to be overweight and 8% were obese.

The findings suggest that weight problems tend to persist during adolescence. Among those who had been classed as obese at the age of 13, 65% were still obese at the age of 17/18. Just 9% had managed to move to the non-overweight category.

Meanwhile, the research also found that while 76% of 17 and 18-year-olds had normal blood pressure, 22% were in the intermediate category, while 2% had high blood pressure. Not surprisingly, those who were overweight or obese were much more likely to have intermediate or high blood pressure.

When it came to mental health, 17 and 18-year-olds appeared to be generally satisfied with their lives, although those from poorer backgrounds were less satisfied.

Most of the teenagers reported positive relationships with their parents, although 10% admitted that they often or always felt let down by a parent.

Around 10% had been diagnosed with anxiety and/or depression by a medical professional and 17% admitted to self-harming at least once. Among these, one in 10 had self-harmed in the last year and girls were twice as likely as boys to self-harm.

The research also looked at education and found that the vast majority of 17 and 18-year-olds were still in school or in higher education. Just 2% were not in education, training or work.

While most of the teenagers said that their teachers were friendly and they could talk to them if they had a problem, 24% said that they ‘disliked being at school'.

Attitudes appeared to vary depending on the teenager's social status. Those from the most socially disadvantaged backgrounds were much more likely to dislike school than those from the most socially advantaged backgrounds.

The research also noted that educational performance from the age of nine was consistently linked to the mother's education. Those whose mothers were more educated tended to score better in maths and English at the ages of nine and 13, and also in Junior Cert exams.

The research also found that most 17 and 18-year-olds had consumed alcohol by this stage and those who had started drinking in their early teens were more likely to be frequent drinkers and to consume more alcohol by the age of 17/18.

Some 12% of 17 and 18-year-olds said they smoked occasionally and 8% said they smoked daily. Those from poorer backgrounds were much more likely to smoke. Meanwhile, just over one in three had tried e-cigarettes.

At least two in three had never tried cannabis, but 8% said they used it occasionally and 2% said they used it ‘more than once a week'.

"The importance of the Growing Up in Ireland study is that it provides very detailed and often sensitive information from nationally representative samples of children in order to highlight the areas of young people's lives where they most need support.

"A significant finding from this research is the importance of early interventions in behaviours that compromise health, such as smoking and alcohol consumption. Drinking alcohol or smoking at an early age is associated with more frequent and higher levels of consumption by the age of 17/18, which points to clear ways we can help teenagers to make healthier choices," commented Prof James Williams of the Economic and Social Research Institute (ESRI), which led the research.

The results were launched at the Growing Up in Ireland Annual Research Conference in Dublin's Croke Park.