 Since the commercialization of marijuana in Colorado, its use among adolescents and young adults has increased significantly, up to a 50% increase reported in a single year. And according to the American Academy of Pediatrics, marijuana is not a benign drug for teens. The teen brain is still developing, and marijuana may cause abnormal brain development, which is why they and the Academy of Child and Adolescent Psychiatry have officially opposed legalization, whereas adult users appear comparatively immune to cannabis-induced long-term changes in brain function and structure. The same cannot be said of those starting during their early teens when effects are both more severe and more long-lasting. During puberty, parts of the brain are actually reorganizing themselves, making this a vulnerable period. Remarkably, the brain does not complete development until approximately age 25. Okay, but is this just reefer madness revisited? Show me the data. Yeah, studies of long-term heavy users tend to show they perform worse on various tests, but how do we know they weren't that way before they even started using? And then, of course, here you are demonstrating they have memory impairments, and yet you're relying on their answers in terms of when they started, how much they've smoked over the years. And so what you need are prospective longitudinal investigations, meaning following kids over time before and after to see what's really going on. Even better, you might think, would be a randomized control trial where you force half the kids to smoke, and even if that were ethical, it could merely show that cannabis has the potential to impair cognition. Only a prospective longitudinal study can really get at whether it's actually impairing brain function in the real world and how much. This was the first study ever published, about 100 young adults assessed since infancy, and after controlling for other factors like alcohol use and their brain function before they started smoking, the bad news is that they did find that regular heavy users did do significantly worse in terms of overall IQ, processing speed, and memory. But the good news was that the effects seemed to be temporary. The brains of those who smoked heavily, but then stopped, appeared to start functioning normally again after like three months. So yeah, if you're in school, of course you want to function at your best, but at least there's no permanent brain damage, or so we thought. The average use of these former smokers was only about two years. They were testing them when they were about 18 years old. In this study, they didn't just follow 100 kids, but 1,000 from birth, all the way to age 38. What did they find? They found that same decline in brain function confirmed by reports of trusted friends and family, especially among those who started younger, but here's the kicker. Sensation of cannabis use did not fully restore brain function among those who started in their teens, even if they subsequently quit. So this suggests a true long-standing neurotoxic effect on the adolescent brain, which justifies why public health authorities are so concerned. And it was a global decline in mental function across all five tested domains— executive function, memory processing speed, perceptual reasoning, and verbal comprehensive, consistent with the thought that there's a critical brain development window that you just don't want to mess with. The decline in IQ, about six points, is the kind of brain damage you see with like low-level lead exposure, both of which are potentially preventable. But how? Do we need more dare drug abuse resistance education? Maybe if it wasn't a complete failure. No beneficial effects in terms of changing drug use or even attitudes towards drug use, which appear to be getting more permissive over time. Combined with earlier ages of initiation. And so increasing efforts should be directed towards delaying the onset of cannabis use by young people, at least until adulthood.