Many years ago, in the 1930s cult classic Reefer Madness, marijuana users were portrayed as violent hooligans. More recent (and more scientific) examination of marijuana and brain damage suggests that for young people, there are concerns. Studies suggest that marijuana could cause significant and irreparable damage. In some cases, the symptoms resemble schizophrenia,. This, according to a new study published in Schizophrenia Bulletin. To dig deeper, a series of MRI scans from the brains of young men who smoked marijuana heavily as teenagers was done. Scientists at Northwestern University’s Feinberg School of Medicine discovered two interesting findings: Of those studied, they discovered that the former pot smokers, now in their early twenties, had developed “abnormalities” in regions of the brain associated with short-term memory. To be more specific, they observed obvious changes to the thalamus, the “Grand Central Station” of neuro-information, which showed that it was now oddly shaped among study subjects. “Both of the groups [we studied] that had a history of marijuana use demonstrated reduced or impaired performance on memory tasks,” notes lead study author Matthew Smith, Ph.D. Second, and more disturbingly, they found that the abnormally shaped brains looked like brains that had been damaged by schizophrenia. For pot smokers already diagnosed with the mental disorder, damage to the thalamus seemed even more severe, making the illness all the more acute. The studies cannot definitively prove that smoking weed could lead to mental illness. Smith, who led the studies, notes that no extreme conclusions can be made and was quick to point out that more studies are needed to link marijuana and brain damage. Despite this, some findings were fairly conclusive. First, smoking weed does affect your short-term memory, including limiting your ability to process information. This could lead to poor performance at work or school, and might also limit your ability to retain information long-term. Second, marijuana could exaggerate your susceptibility to mental illness: “If you have a family history of schizophrenia and you chronically use marijuana, your risk for developing schizophrenia goes up,” says Smith. Another researcher, San Francisco Health Officer Dr. Tomas Aragon, noted a greater susceptibility to young people (millennials) and went so far as to say“Delaying cannabis consumption is the smart thing you can do for your brain, which is still developing into your 20s.”
The warnings about marijuana and brain damage do have scientific research backing their claims. Although researchers still cannot define the exact effects of marijuana use, mounting evidence does suggest the drug may affect younger brains differently than older brains. While the science is still not definitive, it is clear that individuals who use marijuana during adolescence are more likely to develop a substance dependency, schizophrenia and have a lower IQ later in life than individuals who abstain from the drug until they are older. The reason for these associations is not entirely clear, but other research has shown that heavy marijuana use for long periods of time can change connections in brain structure and significantly lower grey matter volume. However, it’s not clear if these brain changes are only in individuals who started using during adolescence, or if these changes are related to any real life behavior differences. One hypothesis suggests that THC, the main psychoactive drug in marijuana, affects and alters something called the “endocannabinoid” system in teenagers. This system controls a number of important behaviors such as neuro-development, stress response and emotions, The American Psychological Association reported. Researchers already note that this system responds to THC, but in young adults, it is still forming. As such, the neurological response to THC could be more disruptive to the developmental process. Despite some scientific uncertainty, many doctors and researchers agree that enough evidence exists to suggest that teens should abstain from the drug until later in life. “There are a lot of open questions” about the long-term effects of marijuana and brain damage, said Susan Weiss, Ph.D., director of the division of extramural research at the National Institute on Drug Abuse, the American Psychological Association reported. “But there’s a growing literature, and it’s all pointing in the same direction: Starting young and using frequently may disrupt brain development.”
We know that being high impairs attention, memory and learning. Some of today’s stronger varieties can make you physically ill and delusional. But whether marijuana can cause lasting damage to the brain is less clear.
A slew of studies in adults have found that nonusers beat chronic weed smokers on tests of attention, memory, motor skills and verbal abilities, but some of this might be the result of lingering traces of cannabis in the body of users or withdrawal effects from abstaining while taking part in a study. In one hopeful finding, a 2012 meta-analysis found that in 13 studies in which participants had laid off weed for 25 days or more, their performance on cognitive tests did not differ significantly from that of nonusers. But scientists are less sanguine about teenage tokers. During adolescence the brain matures in several ways believed to make it more efficient and to strengthen executive functions such as emotional self-control. Various lines of research suggest that cannabis use could disrupt such processes. For one thing, recent studies show that cannabinoids manufactured by our own nerve cells play a crucial role in wiring the brain, both prenatally and during adolescence. Throughout life they regulate appetite, sleep, emotion, memory and movement—which makes sense when you consider the effects of marijuana. There are “huge changes” in the concentration of these endocannabinoids during the teenage years, according to neurologist Yasmin Hurd of the Icahn School of Medicine at Mount Sinai, which is why she and others who study this system worry about the impact of casually dosing it with weed Brain-imaging studies reinforce this concern. A number of smaller studies have seen differences in the brains of habitual weed smokers, including altered connectivity between the hemispheres, inefficient cognitive processing in adolescent users, and a smaller amygdala and hippocampus—structures involved in emotional regulation and memory, respectively. More evidence comes from studies involving animals. With rats who were given THC, the chemical that is responsible for the high in marijuana, show persistent cognitive difficulties if exposed around the time of puberty—but this was not the case if they were exposed as adults. But the link between marijuana and brain damage is not an airtight case. It’s important to note that studies in rats tend to use much higher doses of THC than even a committed pothead would absorb, and rodent adolescence is just a couple of weeks long—nothing like ours. With brain-imaging studies, the samples are small, and the causality is uncertain. It is particularly hard to decipher factors such as childhood poverty, abuse and neglect, which also make their mark on brain anatomy and which correlate with more substance abuse, notes Nora Volkow, director of the National Institute on Drug Abuse and lead author of a superb 2016 review of cannabis research in JAMA Psychiatry. To really sort this out, we need to look at kids from childhood to early adulthood to really understand the potential links between marijuana and brain damage. The Adolescent Brain Cognitive Development study, now under way at the National Institutes of Health, should fill the gap. The 10-year project will follow 10,000 children from age nine or 10, soaking up information from brain scans, genetic and psychological tests, academic records and surveys. Among other things, it should help pin down the complex role marijuana seems to play in triggering schizophrenia in some people. But even if it turns out that weed does not pose a direct danger for most teens, it’s hardly benign. If, like those kids outside my window, you frequently show up high in class, you will likely miss the intellectual and social stimulation to which the adolescent brain is perfectly tuned. This is the period, Volkow notes, “for maximizing our capacity to navigate complex situations,” literally building brainpower. On average, adolescents who partake heavily wind up achieving less in life and are unhappier. And those are things a teenager might care about.