Violence and other anti-social behaviour among Grade 7 to Grade 12 students in Ontario has dropped significantly over the past two decades, according to one of the longest-running mental-health studies of its type.

In addition, results from the latest Ontario Student Drug Use and Health Survey being released Wednesday show a sharp overall drop in bullying, although cyberbullying remains a consistent problem.

"This decline in risk behaviours over time parallels the declines seen in drug-using behaviours ... suggesting a wider cultural shift to less externalizing or rebellious behaviours among young people today compared with previous generations," the researchers from the Centre for Addiction and Mental Health say.

"Ongoing monitoring will determine whether these trends reflect more enduring changes or temporary fluctuations."

Other findings include 81 per cent of students saying they like school to some degree, with nearly half liking school quite a lot or very much.

The survey of students has been done every two years since 1977, making it the longest ongoing school survey of adolescents in Canada and one of the longest in the world, the researchers say. More than 11,000 students in Grade 7 through 12 from 214 schools took part in last year's edition.

Depression, anxiety up among female students

One of the most dramatic changes uncovered by the survey relates to the prescription of opioid pain relievers to students — an important finding given the current addiction and overdose crisis that has killed tens of thousands of people across North America in recent years. Over the past decade, medical use of prescribed opioids among students has plunged to 18 per cent from 41 per cent, the survey finds.

Among concerning trends, the survey indicates a growing number of the students — particularly girls — have symptoms of depression and anxiety. In fact, the study finds, slightly more than half of female students in Ontario show signs of moderate to serious psychological distress — the first time that threshold has been crossed since the survey started tracking the issue in 2013.

"Female students are more than twice as likely than males to report elevated stress, poor mental health, seeking mental health counselling, thoughts of suicide, and being prescribed medication for anxiety or depression," said Dr. Hayley Hamilton, the survey co-lead.

While 19 per cent of students rate their mental health as fair or poor — sharply higher since 2007 — more than half say theirs is very good or excellent.

Nexus of tech and mental health

A key question for further research is the impact of technology on students' well-being, in particular in light of the surge in time spent on social media in recent years.

In total, 20 per cent of students said they spent five or more hours on social media a day — almost double the finding in 2013. One in 20 high school students reported symptoms suggesting they had a serious problem with technology — such as a loss of control, withdrawal symptoms, and issues with family and friends.

"While the survey can't tell us whether technology use causes mental health issues, or vice versa, there is some evidence from other studies that there may be a link," said Dr. Robert Mann, also survey co-lead.

When it comes to bullying at school, about one in five students reported being victims — down sharply from one in three since 2003. However, the same number reported being cyberbullied — unchanged from previous surveys.

For the first time, the survey asked about concussions. More than one-third reported the injury in their lifetime, and 15 per cent — about 130,700 students — said they had experienced one in the past year — invariably from playing hockey or another team sport.

The study also turned up marked differences between girls and boys. For example, males are much more likely to engage in daily physical activity and get at least eight hours of sleep. They are also more likely to be anti-social, gamble, or spend excessive hours playing video games. Girls, however, are more likely to report inferior mental and physical health, physical inactivity, and fears of harm at school.