Conference Coverage

Cannabis crimps teen cognitive development



– What would you predict has a greater detrimental effect on adolescent cognitive development: alcohol or cannabis use?

Dr. Patricia Conrod is a professor of psychiatry at the University of Montreal Bruce Jancin/MDedge News

Dr. Patricia Conrod

The evidence-based answer may come as a surprise. It certainly did for Patricia Conrod, PhD, who led the large population-based study that addressed the question.

“Generally, we found no effect of alcohol on cognitive development, which was a huge surprise to us. It might be related to the fact that the quantity of alcohol consumption in this young sample just wasn’t high enough to produce significant effects on cognitive development. But, to our surprise, we found rather significant effects of cannabis use on cognitive development,” she said at the annual congress of the European College of Neuropsychopharmacology.

Indeed, cannabis use proved to have detrimental effects on all four cognitive domains assessed in the study: working memory, perceptual reasoning, delayed recall, and inhibitory control, reported Dr. Conrod, professor of psychiatry at the University of Montreal.

Her recently study, published in the American Journal of Psychiatry, included 3,826 seventh-grade students at 31 Montreal-area schools. They constituted 5% of all students entering that grade in the greater Montreal area. Participants were prospectively assessed annually for 4 years regarding their use or nonuse of alcohol or cannabis and also underwent neurocognitive testing on the four domains of interest. The assessments were done on school computers with preservation of student confidentiality. Investigators used a Big Data approach to model the relationship between the extent of substance use and neurocognitive function variables over time.

Abstinent students were the best performers on the neurocognitive testing. Cannabis use, but not alcohol, in a given year was associated with concurrent adverse effects on all four cognitive domains. In addition, cannabis use showed evidence of having a neurotoxic lag effect on inhibitory control and working memory. This took the form of a lasting effect: A student who reported using cannabis 1 year but not the next showed impairment of inhibitory control and working memory during both years. And a student who used cannabis both years was even more impaired in those domains.

Dr. Conrod found the evidence of a neurotoxic effect of cannabis use on inhibitory control to be of particular concern because in earlier studies she established that impaired inhibitory control is a strong independent risk factor for subsequent substance use disorders.

”So what we’re seeing is indeed that early onset substance use is interfering with cognitive development, which now sets us up to be able to answer the question of whether evidence-based prevention protects cognitive development by delaying early onset of substance use. And over the longer term, does that protect young people against addiction?”

Dr. Conrod and her coworkers are now in the process of obtaining answers to those questions in the large ongoing Canadian Institutes of Health Research-funded Co-Venture Trial. This randomized trial involving thousands of adolescent students used the investigators’ Preventure Program, a school-based, personality-targeted intervention for prevention of substance use and abuse.

The Preventure Program involves two 90-minute group sessions of manual-based cognitive-behavioral therapy. Students are invited to participate if they score at least one standard deviation above the school mean on one of four personality traits that have been shown to increase the risk of substance misuse and psychiatric disorders. The four personality traits are sensation seeking, impulsivity, anxiety sensitivity, and hopelessness. Typically, about 45% of students met that threshold, and 85% of those invited to participate in the program volunteered to do so. Students of similar personality type are grouped together for the targeted therapy sessions.

This brief coping skills intervention has been shown in multiple randomized trials around the world to reduce the likelihood of substance use in at-risk adolescents. For example, in an early trial involving 732 high school students in London, participation in the Preventure Program was associated with a 30% reduction in the likelihood of taking up the use of cannabis within the next 2 years, an 80% reduction in the likelihood of taking up cocaine, and a 50% reduction in the use of other drugs (Arch Gen Psychiatry. 2010 Jan;67[1]:85-93).

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SOURCE: Conrod P. Am J Psychiatry. 2018 Oct 3. doi: 10.1176/appi.ajp.2018.18020202.

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