How Does Marijuana Influence Adolescent Brain Development?

By Laura Stack

The cartoon of Johnny aiming for a mailbox with a bat while driving in the back of a speeding car pretty much depicts the lack of judgment characteristic of a yet-undeveloped adolescent prefrontal cortex.

As America’s #1 most-used illicit drug and #2 most-popular substance after alcohol, marijuana has been subject to a wide battery of medical studies over the past few decades. In recent year, studies have shown its effects can be devastating, both in the short- and long-term. The biggest problem we worry about at Johnny’s Ambassadors is the severe effects on the adolescent human brain. It can stunt mental development in users, leading to lifelong deficits.

Mental Development in Adolescents

One of the tradeoffs of having big brains is that we humans are born earlier than is optimal, leading to continued brain development outside the womb. Brain development continues until our mid- to late-20s. Like just about everything else, it kicks into high gear during puberty, so kids aged 12-18 are at especially high risk for anything impacting their physical and mental development. And there’s no doubt marijuana impacts mental development in young people, which is also why it’s illegal until the age of 18 (at least proponents acknowledge this science).

While results may vary from person to person, we know that regular marijuana use can result in cannabis-induced anxiety; depression; and suicidal ideation; psychosis; paranoia; and schizophrenia. One study of 45,000 Swedish military conscripts demonstrated that those who used marijuana more than 50 times before age 19 proved six times more likely than the norm to develop schizophrenia by age 34.

The mechanism causing these effects isn’t entirely understood, but apparently, repeated cannabis use in teens interferes with the development of the prefrontal cortex, the part of the brain directly behind the forehead. This area of the brain, the last to develop, is particularly active in adolescence, as the brain prunes some synaptic connections and firms up those most useful to survival. Meanwhile, it refines its use of brain chemicals in preparation for the transition to adulthood. The PFC handles decision-making, planning, impulse control, paying attention, and complex behavior, including executive function—something like the foreman in a factory, who tells people what to do and how to do them. It also helps determine adult personalities and social abilities. For all these reasons, the teen mind is therefore vulnerable to biochemical alteration that prevents it from produces its own natural compounds and growing correctly. Ultimately, marijuana interferes with the child-to-adult transition process; studies have shown adolescents stay “stuck” in that regard at the age of first use.

How It Happens

The way marijuana generates a high is different than how most intoxicants work. In addition to their devastating psychological effects, drugs like heroin and cocaine cause physical damage to the brain, some of which may result in addiction and lasting impairments. Marijuana, on the other hand, hijacks an existing brain process. We all possess natural brain chemicals called endocannabinoids. Marijuana compounds mimic them with 85+ cannabinoids, especially the cannabinoid THC, which produces the “high.” Our natural endocannabinoid system helps us manage stress, pain, mood, anxiety, and fear. Endocannabinoids also play a role in fetal and adolescent mental development.

Because they’re a part of our natural neurochemical arsenal, our neurons already have receptors where endocannabinoids fit and go to work. THC takes over these chemical receptors, resulting in a high because they disrupt their natural function. If this happens too often, they can alter and block important functions, including the transmission of a neurochemical called GABA that plays a big role in inhibition. Basically, it stops you from doing impulsive things, like, smoking more weed. If the endocannabinoids can’t find their homes because THC already occupies them, the brain may automatically start producing fewer endocannabinoids—or none at all—and then you have to use more and more marijuana to achieve the same high. This process inevitably stunts mental growth as your own brain no longer creates its own chemicals. So when you abuse marijuana as a teen, your own mind eventually turns on you.

The Final Negative Influence

The problem here is getting young people to understand and actually worry about what might happen to them if they use marijuana. This is one of THC’s most underestimated effects on adolescent brain development. Because teens don’t understand how THC talks their bodies into betraying them, they don’t see it as a major threat the way heroin or cocaine is. Worse, they use it because they consider it a low-risk gamble since “all of my friends are using it.” Most adults may think their kids don’t understand the potential effects of early marijuana use, but in many cases they do. They just aren’t worried about anything happening to them. Teens feels invincible, due to their PFC not being formed. They know that unlike harder drugs, not everyone gets addicted to marijuana or has lingering effects. They also know it has a very low death toll.

One developmental neuroscientist, Kuei Y. Tseng, often addresses young people about the negative effects of THC, and he points out that all they really want to know is how much they can consume without harming their brains—something he can’t quantify. Scientists have concluded there is no safe amount of marijuana during adolescent brain formation.

In an advisory released August 29, 2019, the US Surgeon General went so far as to state that “until and unless more is known about the long-term impact, the safest choice for pregnant women and adolescents is not to use marijuana.” Former US Food and Drug Administration (FDA) commissioner Scott Gottlieb said he had significant concerns about the “great natural experiment we’re conducting in this country by making THC widely available,” citing his fears about “the impact that this has on developing brains.”

Most urgently, we must educate parents and teens about the dangers of today’s high-THC marijuana on the developing adolescent mind. That’s our mission here at Johnny’s Ambassadors. We are developing an online curriculum to help teens and their parents understand what a deceptive threat pot really is. It can leave you with a lifetime of crippling mental illness, which can be hard to worry about it if you can’t imagine it.

Believe me, my son Johnny couldn’t imagine it. He thought it would never happen to him. Those who have never experienced delusional thoughts that the mob is after you can’t understand how awful it can be. Please don’t risk finding out.

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