The findings are contained in research by the ESRI and HSE which analyses how young people receive information on sex and relationships.
It is based on data from Growing up in Ireland, a longitudinal study which interviewed teenagers at 13 and 17 years of age.
Many teens are not getting advice on sex from their parents, the report shows.
By age 13, 45 per cent of young people reported that they had discussed sex and relationship issues with their parents. By age 17, this proportion had increased to just under 60 per cent.
There was a gender divide in reports of ease of discussions with parents about sex.
Young women found it easier to talk to their mothers, while young men found it easier to talk to their fathers.
Young people who discuss sex and relationships with their parents are significantly more likely to go on to use contraception.
In contrast, those mainly reliant on their friends as a source of information on sex had lower levels of contraceptive use when they first had sex.