School-based interventions can prevent or delay cannabis use in teens, according to a new study by University of Montreal and CHU Sainte-Justine Children's Hospital.

At-risk teens who smoke marijuana are more likely to experience neurocognitive deficits, reduced educational and occupational attainment, motor vehicle accidents, and precipitation of psychosis.

"Marijuana use is highly prevalent among teenagers in North America and Europe," Dr. Patricia Conrod, who led the study, said in a statement. "As attitudes and laws towards marijuana are changing, it is important to find ways to prevent and reduce its use amongst at-risk youth. Our study reveals that targeted, brief interventions by trained teachers can achieve that goal."

Previous studies have shown that teens who have used marijuana have been shown have less ability to sustain their attention and control their impulse control and have impaired cognitive processes.

For the study, researchers collected and analyzed data from more than 1,000 high-risk British students and their teachers at 21 secondary schools in London. The children selected for the study identified as being at high-risk by their responses to a clinically-validated personality assessment. People who are sensitive to anxiety or negative thinking, or who are impulsive or sensation-seeking are known to be at greater risk of substance abuse.

Approximately 25 percent of high risk youth took up cannabis use over the course of this two-year trial. The intervention was associated with a 33 percent reduction in cannabis use rates within the first six months after the intervention and then reduced frequency of use another six months later.

"Within the group at greatest risk for cannabis use, sensation seekers, the intervention was associated with a 75 [percent] reduction in rates of cannabis use six months post intervention, as well as significant reductions in frequency of use thereafter," Dr. Conrod exclaimed.

The findings are detailed in the journal Addiction.