OTTAWA — Canada's 15-year-olds are among the world's No. 1 teen pot smokers, according to an expansive new drug and alcohol study funded by Health Canada.

The work by Carleton University researchers found about half of Grade 10 students have used marijuana at least once, up from one-third in 1990.

That places Canadian 15-year-olds first in age-related cannabis use among 43 countries and regions participating in the World Health Organization's collaborative Health Behaviour in School-aged Children (HBSC) study.

The Carleton researchers conclude: "The proliferation of cannabis use in this population suggests a need to monitor this trend closely and its potential consequences for cognitive and psychomotor functioning and related risk behaviours."

Meanwhile, the study found alcohol use and drunkenness dropped slightly among youths 12 to 17 years old.

The research, results of which are to be published in the April edition of the Canadian Journal of Psychiatry, is the first time nationally representative samples gathered over several years have been used to estimate drug and alcohol use among Canadian adolescents. Previous research relied largely on one-time, provincial and regional surveys.

The new work, led by Frank J. Elgar in Carleton's psychology department, is based on five HBSC surveys of Canadian adolescents every four years from 1990 to 2006, about 30,000 students in all. Results from 2002 and 2006 also were compared to international HBSC data.

Among the findings:

- In 1990, about 25 per cent of Grade 10 students reported using marijuana at least once. By 2002, that figure rose to 45 per cent, then dropped to 38 per cent in 2006.

- Lifetime prevalence of Canadian Grade 10 students using other drugs, such as cocaine, remains below 10 per cent.

- Since 1990, a relatively consistent percentage of about eight per cent of Grade 10 students used prescription drugs or over-the-counter medications to get high, dropping to five per cent in 2006.

- In all five national surveys, most Grade 10 students reported being drunk at least once, while about one-third of Grade 8 students and one-tenth of Grade 6 students admitted to what they considered drunkenness.

- From 1990 to 2006, the percentage of students in all grade levels who have been drunk at least once decreased by about seven percentage points: from 61 per cent to 54 per cent in Grade 10 students, from 34 per cent to 27 per cent in Grade 8 students, and from 13 per cent to six per cent in Grade 6 students.

- The Canadian Institutes of Health Research and the Social Sciences and Humanities Research Council of Canada provided additional research funding.