Let’s go ahead and say it’s common sense not to let teenagers smoke cannabis. Now let’s remember that teenagers have no common sense (it hasn’t grown in yet—along with the rational part of the brain).This isn’t (just) snark talk from an old man, though. Current common sense has extended “childhood” into the mid-20s. That’s because the brain isn’t fully matured until around age 25. And the last thing to develop is the prefrontal cortex—the part of the brain associated with decision-making, planning complex behavior and moderating social behavior, among other things.Which sounds like some kind of sick cosmic joke. When a teen does something stupid, and someone asks angrily, “What the hell were you thinking?” and they shrug and say, “Uhdunno”—they aren’t lying. They really have no idea.According to Sandra Aamodt, neuroscientist and co-author of the book Welcome to Your Child’s Brain, 18-year-olds are only about halfway through the process of developing their prefrontal cortex. On top of that, their reward system is more active around the time of puberty and slowly lowers to adult levels around 25, so they’re more likely to enter into risky situations and bend to peer pressure. Pediatric neurologist Frances Jensen, author of The Teenage Brain, says human frontal lobes aren’t connected until the mid-20s, making communication between them slow and inefficient. This results in poor decision-making skills and makes it harder to think about the effect of one’s actions on others. Sound familiar?But I’m not just harping on teens for no reason. In early October The American Journal of Psychology published “A Population-Based Analysis of the Relationship Between Substance Use and Adolescent Cognitive Development.”The study followed 3,826 seventh grade students from 31 Montreal schools over 4 years. They were told that their parents and teachers would never have access to the study’s data (smart move) and were asked to give annual reports on their alcohol and marijuana use. They were also assessed yearly on recall memory, working memory, perceptual reasoning and inhibition. The assessments were made using computer cognitive tests. The results were a little surprising. Around 75 percent of the students reportedly consumed alcohol at least occasionally while 30 percent used cannabis. According to the study, even irregular cannabis use in teens could do more damage to long-term cognitive abilities than alcohol. While alcohol had its own deleterious effects on cognition, marijuana use showed neurotoxic effects on inhibitory control (affecting the ability to manage addiction) and working memory, independent of alcohol use. Worse still, there were “lagged effects” associated with cannabis that showed up years after discontinuing use.This study seems to answer some questions we’ve all had about the effect of marijuana on the developing mind, but I’ve already met resistance to the idea—mostly from friends who, like myself, used cannabis as teenagers. The idea that we might have significantly damaged our brain development is the bitterest of pills.But it’s also not the final word. JAMA Psychiatry just published “Association of Cannabis With Cognitive Functioning in Adolescents and Young Adults” in June, and it found that while there was a “small but significant overall effect size for reduced cognitive functioning in adolescents and young adults” who used cannabis regularly, “abstinence of longer than 72 hours diminishes cognitive deficits.” And that one was a meta-analysis of 69 cross-sectional studies utilizing 2,152 cannabis users and 6,575 comparison participants. So maybe there’s hope for those of us who started too soon after all. Just look at me. My brain works at least half of the time.But until it’s further studied, of course, the smart thing would be to educate the teens in your life about the possible dangers and try to communicate that waiting is the safest option. (Good God, can you remember being a teenager and having to wait for anything? It was the absolute worst. Remember abstinence programs? Hilarious.)Especially considering cannabis seems to have multiple mechanisms that could hamper a young person’s ability to ward off addictive tendencies. In the context of an opioid overdose epidemic, the mere possibility should be enough to make one cautious.
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