A survey of more than 10,000 Ontario high school students found more than a quarter were given the go-ahead by their parents to drink alcohol at home with friends, something that concerns one of the study's authors, who says that could increase the chances that young people will drink to excess.

The Centre for Addiction and Mental Health's Ontario Student Drug Use and Health survey started in 1977 and is given to students in grades 7 through 12 every two years. The 2015 results on 10,426 students in the province were released on Wednesday.

Student drinking rates have declined over the long term, but hazardous drinking continues to be a concern, said Dr. Robert Mann, a senior scientist at CAMH and co-lead investigator of this year's study.

For the first time, investigators asked high school students if their parents allowed them to drink at home. About 27 per cent answered yes.

"We were surprised by this number," Mann said in a news release. "It suggests some parents might think it's safer to supervise kids while they drink. In fact, other research shows that students who are allowed to drink at home are more likely to drink excessively."

Girls and boys were equally likely to report drinking. But the answers varied by grade, ranging from nine per cent of students in Grade 9 to 38 per cent in Grade 12, the researchers said.

As many as one in five high school students reported hazardous drinking, a risky pattern that can cause current or future physical, psychological or social problems.

An estimated 19 per cent of students reported binge drinking – defined as having five or more drinks on one occasion – at least once in the month before they filled in the survey, a finding Mann said he's concerned about.

The survey also asked about use of:

  • Cannabis – one in five students in grades 7 to 12 reported using marijuana in the previous year.
  • Electronic smoking devices, or vaping – More students used e-cigarettes than tobacco cigarettes. Nine per cent of students in grades 7 to 12 said they smoked regular cigarettes during the past year, while 12 per cent said they had more than a few puffs of an electronic cigarette, with or without nicotine.
  • Non-medical use of prescription opioids — Reported abuse of painkillers such as codeine dropped significantly from 21 per cent in 2007, the first year of monitoring, to 10 per cent in 2015.
  • Ecstasy - The reported use of ecstasy increased from three per cent in 2013 to more than five per cent in 2015, with a greater increase among females than males.

During the 2014-15 school year, 10,426 students from across Ontario in grades 7 to 12 participated in the survey, administered on behalf of the hospital by the Institute for Social Research at York University.