The Impact of THC on the Teen Brain: A Vulnerable Stage

The majority of teenagers correctly recognise the high risk of harm associated with regular use of substances like cigarettes, alcohol, cocaine and heroin. However, many overlook one common substance - cannabis.

Results from the National Survey on Drug Use and Health reveal that only 35 percent of 12- to 17-year-olds perceive a significant risk of harm associated with smoking marijuana once or twice a week. This viewpoint may also be held by their parents, who may be under the assumption that today's cannabis products are the same as those they might have known during their youth. According to Kelly Young-Wolff, licensed clinical psychologist and research scientist at Kaiser Permanente Northern California Division of Research in Oakland, some parents might think that cannabis use isn't as harmful as other drugs.

But today's cannabis products are exponentially more potent and can increase risks for addiction and psychosis. Over the years, marijuana plants have been cultivated to contain more delta-9-tetrahydrocannabinol (THC), the main psychoactive compound. In 1995, the THC content in marijuana was around 4 percent; currently, it can surpass 20 percent. Even more potent are concentrated cannabis products, such as wax, budder and shatter, with their THC content reaching a staggering 95 percent.

Recreational cannabis use is currently legal for adults in 24 states and Washington, D.C., and has medical acceptance in 38 states and D.C. The increased accessibility of cannabis has created a false sense of safety around its use. Pediatrician Beth Ebel of the University of Washington School of Medicine and Seattle Children’s Hospital highlights that this is a misguided assumption. Especially for younger individuals, THC can significantly impact brain chemistry, leading to lifelong health consequences.

Neuroscientist Yasmin Hurd of the Icahn School of Medicine at Mount Sinai in New York City suggests that the extremely potent concentrated cannabis products should perhaps be classified differently. She calls them “new drugs.”

Adolescence is viewed as a particularly vulnerable time for cannabis use. The adolescent brain undergoes significant development and reorganisation into early adulthood, a process THC can negatively impact. Hurd notes that during this stage, the brain determines what’s important to learn and retain.

THC interacts with the endocannabinoid system, especially the main CB1 receptor. This system plays critical roles in brain development and regulates diverse functions such as anxiety, pain, memory and behavior. THC's impact can disrupt this crucial signaling, leading to lasting alterations in the brain structure.

Research on animals suggests exposure to THC in adolescence can lead to a reduction in CB1 receptors, causing long-term issues with memory and learning. It can alter the prefrontal cortex, which is important for problem-solving and emotional regulation. A study conducted on adolescent rats unveiled that THC caused premature disruption of connections in the prefrontal cortex.

Parallel impacts were seen in research on human teens. An analysis of brain scans from around 800 adolescents at 14 and 19 years showed that cannabis use over five years was associated with accelerated thinning of the prefrontal cortex. This thinning typically occurs in adolescence due to the pruning of less used connections. However, the accelerated thinning observed suggests a deviation from normal brain development, which might be linked to premature loss of nerve cell connections similar to the rat study.

Cannabis use in adolescents places them at a higher risk of developing mental health issues, even when taken recreationally. The risk is more profound in adolescents between 12 and 17 who use cannabis but do not qualify for a substance use disorder, as they are two times more likely to become depressed or express suicidal thoughts. This was inferred from research conducted on over 68,000 teenagers and published in May in JAMA Network Open.

A more severe condition, cannabis use disorder, occurs when a person's daily life is negatively impacted by cannabis and they are unable to quit. In such cases, the likelihood of depression and suicidal thoughts is 2.5 to 3 times higher than in adolescents who do not use cannabis. This was also reported in the JAMA Network Open study.

Teenagers diagnosed with cannabis use disorder or those who use it recreationally have a higher percentage of depression and suicidal ideation than those who do not use cannabis.

The risk of dependence increases when cannabis use begins during adolescence as opposed to adulthood, just like other substances such as alcohol, cocaine, and nicotine. Compared to young adults, adolescents are more likely to become dependent within a year of their first usage. These findings were reported in a 2021 study published in JAMA Pediatrics.

Despite these risks, many teenagers are resorting to cannabis as a means to cope. Their motivations are often related to escapism or managing emotions, and these reasons have doubled in occurrence over the past four decades, according to a study published in the Journal of Studies on Alcohol and Drugs in 2019.

The behavior of using cannabis can set a detrimental course for a teen’s future. A study comparing cannabis usage before age 17 and life outcomes at age 30 found habitual users were more likely to become dependent on cannabis, use other drugs and attempt suicide, and less likely to finish high school. This study was published in Lancet Psychiatry in 2014.

There is a concerning correlation between cannabis addiction and the onset of schizophrenia, especially in males, as found in a study of nearly 7 million Danes aged 16 to 49.

Though smoking marijuana remains the most common method of intake, the rise in vaping cannabis concentrates is notable. From 2015 to 2018, vaping saw an increase from 26% to 34% amongst users, with daily use more prevalent amongst those who vape. This was published in JAMA Pediatrics in 2020.

Concerns also include indications that high-potency products might increase the risk of psychosis, a symptom of schizophrenia. Furthermore, a Canadian study found a 13-fold increase in emergency department visits due to cannabis hyperemesis syndrome, a complication of high potency cannabis use that leads to abdominal pain, nausea, and repeated vomiting. These high-potency products and their full impacts on health remain largely unexplored and as such, users could be considered as test subjects.

So as with other substances, public health officials recommend that parents talk with their kids about the risks of cannabis use. Especially with indications that teens are turning to cannabis to self-medicate, “if you notice a change in your child’s behavior, try to find out what’s going on,” Young-Wolff says. It’s also important for parents to consider the messages they send about marijuana, she says. The clinicians Young-Wolff has talked to have noticed that parents are using cannabis more and that they’ve become more permissive about teen cannabis use. “That can really make it hard to get this message to the kids to not use,” she says.

So, for adults who are taking part in the new legality of marijuana: “If you are going to use cannabis,” Young-Wolff says, “don’t use in front of your children.”