TORONTO -- Alcohol remains the most popular drug of choice among Ontario youth, according to the most recent biennial survey of Grade 7 to 12 students by the Centre for Addiction and Mental Health.

Almost 46 per cent of the 10,426 respondents from across the province reported having imbibed in the past year, said Robert Mann, a senior scientist at CAMH who co-authored Wednesday's report.

"And that proportion increases with grade, so that by the time students get to Grade 12, we see that slightly over 72 per cent used alcohol in the past year," said Mann, adding that 29 per cent of 12th-graders engaged in what's considered hazardous consumption of booze.

While the overall proportion of students who reported drinking alcohol has dropped substantially in the last two decades -- in 1999, 66 per cent of students said they drank -- about 18 per cent of this year's survey respondents admitted to binge drinking at least once during the previous month.

Binge drinking is defined as having five or more drinks on one occasion, said Mann.

"Binge drinking is dangerous, and we are concerned to see nearly 20 per cent of high-schoolers report blacking out on at least one occasion in the last year."

Also of concern was the finding that about a quarter of those who drank alcohol did so at home with their parents' blessing.

"It's the first time we'd asked that question, and that's not just having a sip of wine on a family occasion," he said. "This is being allowed to drink at home with your friends.

"That number is surprising to me and it is higher than I might have expected. And the large majority of these people are underage."

Mann said researchers aren't sure why some teens are allowed to drink alcohol at home, but it may be because parents believe it's safer if it's done under their supervision.

However, studies suggest that young people who are permitted to tipple at home are more likely to be heavy drinkers, he said.

"I think parents also need to be concerned whether young people are turning this into a pre-drinking session, having the drinks at home and then going out afterwards and drinking more. We know that happens as well."

The survey also found that 20 per cent of Grade 7 to 12 students reported having used marijuana in the past year. Again, usage was found to increase with age; 37 per cent of 12th-graders admitted they used pot.

"It turns out that more students report using cannabis than report using tobacco," said Mann. "And we've seen substantial declines in tobacco use with the implementation of public health controls over the past decade or so, when we have not seen similar kinds of declines with cannabis use.

"So that experience suggests that strict public health controls of cannabis use can ideally achieve the same kind of control that we see with tobacco."

Overall, almost nine per cent of students reported smoking tobacco -- a level that has remained static for the last few years, following a steady decline over the last couple of decades. Prevalence of cigarette smoking reached 15 per cent among Grade 12 students.

However, a higher proportion of students overall -- 12 per cent -- reported puffing on electronic cigarettes, with or without nicotine, compared to tobacco-based smokes.

"These numbers could mean that students are assuming it is safer to use e-cigarettes than tobacco cigarettes," said CAMH scientist Hayley Hamilton, who co-authored the report.

"But the problem is we still don't know if e-cigarettes are safe. Research on the effects of e-cigarettes is in its very early stages and we don't know about longer-term health and safety effects."

Researchers also found that reports of non-medical use of prescription opioids has dropped significantly, to 10 per cent of students in 2015 from 21 per cent in 2007.

"While this trend is certainly positive, 10 per cent of students using highly addictive prescription opioids for non-medical reasons is still far too high," said Mann, noting that most respondents said they obtained the drugs at home, "presumably from the family medicine cabinet."

"I think there's an opportunity for parents to exert some control over the availability of these very powerful drugs."

The Ontario Student Drug Use and Health Survey, conducted every two years since 1977, is Canada's longest-running systematic study of substance use among youth.