“Early alcohol use is associated with a long list of negative health consequences down the line,” said Mahmood Gohari, a public health postdoctoral researcher at Waterloo. “This study reinforces the idea that prevention policies need to start in those first two years of high school, or even before that, before drinking becomes habitual.”

The researchers found that 45 per cent of youth who drank up to three times per month in Grade 9 were likely to become weekly -- or almost daily -- drinkers with some binge drinking episodes the year after.

The students most likely to binge drink were weekly and almost daily drinkers, and Grade 9 students were more likely to transition to binge drinking than Grade 10 or 11 students.

“These findings show there is no such thing as low-risk drinking,” Gohari said. “We need to be concerned about even infrequent rates of alcohol use among youth.”

On the other hand, 66 per cent of non-drinking grade 9 students remained non-drinkers by grade 10. This percentage decreased to 62 per cent a year later, but stayed steady one year after that. The percentage of heavy drinkers remained steady at 18 per cent from Grades 9 to 11, then went up to 25 per cent in Grade 12. 

The researchers also found a link between frequent drinking, cigarettes and cannabis. In Grade 9, youth who used cannabis were six times more likely to report monthly drinking compared to non-drinkers; this increased to almost 10 times at follow-up.

“Access to alcohol is ubiquitous, so it’s important to restrict availability wherever possible,” said Gohari. “It’s one of the top recommendations made by the World Health Organization and others.”

The researchers used data from more than 19,000 students across 89 schools in Ontario and Alberta through the COMPASS study, the largest school youth survey in Canada, and examined alcohol use trajectories among high school students.

The study, “Identifying trajectories of alcohol use in a sample of secondary school students in Ontario and Alberta: Longitudinal evidence from the COMPASS study,” was authored by Mahmood Gohari (Waterloo), Joel Dubin (Waterloo), Richard Cook (Waterloo) and Scott Leatherdale (Waterloo), and was published in Health Promotion and Chronic Disease Prevention.

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