It is well-accepted that chronic, daily marijuana use can lead to memory problems. It is also well-accepted that adolescent users are much more likely to develop problems with short-term memory, attention, and other cognitive deficits than adult users. However, a recent study in The Journal of Clinical Psychiatry published last month provided promising results in that these deficits could be reversed after 1 month of abstinence. The study, conducted by Dr. Randi Schuster, Ph.D., and colleagues out of Massachusettes General Hospital in Boston, recruited adolescent smokers and divided them into abstinent and non-abstinent cohorts. Improvements in short-term memory were seen in the abstinent group in as little as one week of abstinence.
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These are welcome results considering previous studies both in humans and in animal studies which suggested that these cognitive impairments may not be reversible. The part of the brain associated with higher cognitive functioning (e.g. memory, learning, impulse control, and attention) is the prefrontal cortex (PFC). This area of the brain is the last to develop in humans and is not fully formed until about the age of 25. Chronic marijuana use before the PFC is finished developing is a major concern for adolescent mental health.
It is thought that the psychoactive compounds within marijuana (mainly delta-9-tetrahydrocannabinol; THC) interferes with normal neurodevelopment. For example, another animal study found that adolescent treatment with THC impaired spatial memory as adults and also disrupted normal hippocampal structure and function. The hippocampus is critical for memory, especially in forming and maintaining short-term memory. Abnormalities in white matter in the frontal cortex of young chronic marijuana smokers have also been found using brain imaging techniques in humans. These deficiencies can also contribute to declines in cognitive function in adulthood.
Another well-established effect of chronic use in adolescents is an increased propensity to develop various mood disorders, such as anxiety and depression. However, the question of whether these adolescents would have developed these mood disorders in adulthood regardless of marijuana use has yet to be answered. In an ambitious effort by the National Institutes of Health (NIH), researchers are now monitoring children as young as 9 years old in an attempt to answer that question. The plan is to follow this cohort of kids as they grow into adulthood to determine which comes first: the drug use or the mood disorder. So, in about 15 years we may have the answer to that question.
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For now, though, it is comforting to know that not all hope is lost for teenaged users, at least in terms of regaining the ability to retain short-term memories. That is if they choose to remain abstinent. As the percentage of teenaged daily pot users increases, it is imperative to remember that the adolescent brain is not the same as one of an adult. With recreational marijuana use being legalized, more and more companies are (allegedly) marketing to teens. Whether it is through candy-flavored CBD oil or THC-infused gummy bears, more teens now than ever have access to marijuana and its psychoactive compounds. Dispensaries, of course, are not allowed to sell to minors. But that's never stopped them from procuring cigarettes or alcohol; so do we really think they won't be able to obtain this new forbidden fruit?
Sources: www.drugabuse.gov, American Journal of Diseases of Children, The Journal of Clinical Psychiatry, Neuropsychopharmacology, Hippocampus, Experimental and Clinical Psychopharmacology, Alcohol & Drug Abuse Institute - University of Washington, Science, www.aacap.org