Researchers at Northwestern Medicine have found that the developing teenage brain may be particularly vulnerable to excessive marijuana use. In a new study
—published on December 16, 2013—scientists report that teens who smoked marijuana daily for about three years had abnormal changes in their brain structures related to working memory and performed poorly on memory tasks.
It is common sense that being a heavy cannabis user might make someone more spaced-out and less likely to perform well on memory tasks. Excessive chronic use of any type of drug is going to have detrimental mental and physical side effects.
Alarmingly, the brain abnormalities and memory problems were observed during the individuals' early twenties, two years after they stopped smoking marijuana. The researchers found that memory-related structures in their brains appeared to shrink and collapse inward, reflecting a possible decrease in neuron volume. These findings could indicate long-term detriments of chronic marijuana use as a teenager.
Dazed and Confused
Marijuana targets receptors in these brain regions.
Over the past decade, researchers around the world have found that changes in brain structure and connectivity are directly linked to how the brain functions.
This Northwestern study is the first to target key brain regions in the deep subcortical gray matter of heavy marijuana smokers using structural MRI and to correlate abnormalities in these regions with working memory. Working memory is the ability to remember and process information in the moment and the ability to transfer it to long-term memory when needed.
Cannabis use has long been associated with working memory impairments. However, the exact relationship between cannabis use and working memory neural circuitry remains somewhat of a mystery. The Northwestern team examined whether a cannabis use disorder (CUD) was associated with differences in brain structure between control subjects with and without a CUD.
The younger the individuals were when they started chronically using marijuana, the more abnormally their brain regions were shaped, the study reports. The findings suggest that these regions related to memory may be more susceptible to the effects of the drug if abuse starts at an earlier age.
"The study links the chronic use of marijuana to these concerning brain abnormalities that appear to last for at least a few years after people stop using it," said lead study author Matthew Smith, an assistant research professor in psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine. He adds,"With the movement to decriminalize marijuana, we need more research to understand its effect on the brain."
Because this study only examined one point in time, a longitudinal study is needed to definitively show if marijuana is responsible for the brain changes and memory impairment. It is possible that the abnormal brain structures reveal a pre-existing vulnerability to marijuana abuse. But evidence that the younger a subject started using the drug the greater his brain abnormality indicates marijuana may be the cause, according to Matthew Smith.
The Marijuana Abuse and Schizophrenia Connection
The subjects of the Northwestern study started using marijuana daily between 16 to 17 years of age and on average were heavy users for about three years. A total of 97 subjects participated, including matched groups of healthy controls, subjects with a marijuana use disorder, schizophrenia subjects with no history of substance use disorders, and schizophrenia subjects with a marijuana use disorder.
The subjects who used marijuana did not abuse any other drugs. Similar cannabis-related shape differences were observed in the striatum, globus pallidus, and thalamus in controls and schizophrenia subjects.
Previous studies have shown a link between cannabis use in the teenage years and mental illness in later life. Research completed by psychiatrist Professor Robin Murray in 2005 showed that those who smoked the drug regularly at 18 were 1.6 times more likely to suffer serious psychiatric problems, including schizophrenia, by their mid-20s.
For those who were regular users at 15, the stakes were even higher, with their risk of mental illness by the age of 26 being 4.5 times greater than normal. It is thought that, when canniabis is abused during teenage years, the drug can cause permanent damage to the developing brain.
In June 2013, an Australian study found that prolonged use of cannabis or marijuana by young adults was linked to a higher risk of developing psychosis, with the highest risk affecting those who started using the substance in their teens, and continued using it for 6 years or more into adulthood: the risk of developing psychosis among these users was more than double that of those who never used the drug.
Chronic marijuana use could augment the underlying disease process associated with schizophrenia, Smith noted. "If someone has a family history of schizophrenia, they are increasing their risk of developing schizophrenia if they abuse marijuana," he said.
Red arrow points to thalamus.
While chronic marijuana smokers and chronic marijuana smokers with schizophrenia both had brain changes related to the drug, subjects with the schizophrenia had greater deterioration in the thalamus.
The thalamus is a communication hub of the brain that is critical for learning, memory and communications between brain regions. Smith added, "If you have schizophrenia and you frequently smoke marijuana, you may be at an increased risk for poor working memory, which predicts your everyday functioning."
The brain regions examined in this study also affect motivation. For more on ‘amotivational syndrome’ check out my Psychology Today blog post, “Does Long-Term Cannabis Use Stifle Motivation?”
"A tremendous amount of addiction research has focused on brain regions traditionally connected with reward/aversion function, and thus motivation," noted co-senior study author Hans Breiter, M.D., professor of psychiatry and behavioral sciences and director of the Warren Wright Adolescent Center at Feinberg and Northwestern Memorial. "This study very nicely extends the set of regions of concern to include those involved with working memory and higher level cognitive functions necessary for how well you organize your life and can work in society."
Conclusion: Endocannabinoids and "Just Say No 2.0"
John Csernansky, M.D. and co-senior author on the Northwestern study concluded, "The abuse of popular street drugs, such as marijuana, may have dangerous implications for young people who are developing or have developed mental disorders. This paper is among the first to reveal that the use of marijuana may contribute to the changes in brain structure that have been associated with having schizophrenia."
Legalizing marijuana has led to more widespread use. In the United States, marijuana is the most commonly used illicit drug and young adults have the highest—and growing—prevalence of use. Some consider it a harmless drug when used in moderation ... and it has a wide range of medicinal benefits. That said, this study suggests that excessive use of marijuana can alter a teenager's brain development. As parents and caregivers, this study serves as a reminder that it is important that we strive to keep our children from heavily abusing marijuana.
What can we do to stop teenagers from developing a cannabis use disorder? I know there are no easy answers. But as I zealot for the power of daily lifestyle habits to improve brain function, health, and happiness it is worth noting that aerobic exercise releases endocannabinoids which can have many of the same stress-reducing benefits for a teenager who may be smoking marijuana to self-medicate for anxiety.
Also, other daily habits like: maintaining a strong social network, playing a musical instrument, making art, certain types of video gaming, mindfulness training and meditation have all been shown to change brain structure in positive ways that actually improve working memory and fluid intelligence.
In my book, The Athlete's Way I write extensively about the power of endocannabinoids and other neurochemicals to create the runner’s high and state of calmness. Our body naturally makes a wide range of substances endogenously that have receptors throughout the brain which are hijacked by ‘exogenous’ drugs. Endo- means “from within.” Endocannabinoids are your body's own cannabis ... Endorphins are your body's own morphine, etc.
Physical activity and meditation are not a panacea for substance abuse or addiction. However, I believe that if we can get more teenagers rigorously working out their bodies and minds most days of the week—and realizing how great breaking a sweat and meditation makes them feel—many would get in the habit of seeking a daily ‘runner’s high’ or zen-like state of calm instead of developing a cannabis use disorder.
If you'd like to read more on this topic, check out my Psychology Today blog posts:
Follow me on Twitter @ckbergland for updates on The Athlete’s Way blog posts.