This Is Your Teenager's Brain on Pot

Molly Triffin
Molly Triffin

When Elliott, now 19, was a junior in high school, here’s what an average day looked like: He’d wake up at 5:30, shower, get dressed, eat a quick breakfast, and then ride his bike to the bus stop, which was marked by a roughly built wooden hut. Once there, he’d reach up to the roof of the hut, where he’d stashed a bowl and a baggie of marijuana. “I hate school, so I always smoked right before the bus picked me up at 6:20,” Elliott tells Yahoo Beauty. “It calmed me down.”

In the afternoon, he’d finish up his homework and then head out onto the back porch to 420, assured that no one other than his single mom would see him, since he lived on a dead-end street. “My mom doesn’t really care,” Elliott says. “She’d rather I smoke than do heroin.”

His love affair with weed kicked off on Halloween night in 2014, when Elliott, then 16, lit up for the first time with friends. Although he didn’t feel anything, he was still curious, so he tried it again. And the second time, he got high.

“It was pretty great,” Elliott says. “Weed is the best drug because you are in control of yourself and what’s going on.” Elliott claims he hasn’t noticed any negative side effects from marijuana use — and that he could stop anytime he wanted.

Meanwhile, there’s Liz, now 18, who started smoking weed regularly at the age of 12 as a coping mechanism, as she puts it, for the upset she felt around her parents’ divorce.

“At first I kind of just felt, like, very… relaxed, spacey,” she says. “After a while, after I started using day after day, I kind of just felt more lethargic. No motivation for anything. Very apathetic. And I felt, like, a lot of paranoia along with that.” By her early teens, Liz had developed a pot habit — not to mention an eating disorder and a self-harming problem — severe enough to land her in a residential treatment program, the Newport Academy.

“I realized that I had a problem with marijuana when I found that I couldn’t be comfortable when I was sober,” she tells Yahoo, adding that the softening marijuana laws across the country are sending what feels to her like “a mixed message” about the safety of weed.

Many Americans feel similarly conflicted about marijuana and its effects on physical and mental health, caught somewhere between Elliott and Liz. According to a new exclusive Yahoo News/Marist Poll, a slight majority of Americans — 51 percent — think using marijuana poses a health risk, while 44 percent think it does not, and 5 percent remain unsure.

When it comes to teens, that narrative has begun to shift, due to a series of studies pointing out that the vulnerable, still-developing brains of adolescents do not mix so well with marijuana. But definitive research about how cannabis specifically affects teens still remains frustratingly elusive, as for every study out there suggesting that pot has deleterious effects, another analysis affirms its harmlessness.

In fact, the lack of conclusive answers is what triggered the National Institute on Drug Abuse (NIDA) to recently embark upon a large-scale longitudinal study that will track 10,000 adolescents into early adulthood to look at how use of illicit substances, including marijuana, affects their developing brains and shapes their lives.

In the meantime, Yahoo Beauty spoke with top researchers to get as clear a picture as possible of what we do know about weed and the teenage brain.

Why the Teenage Brain Is So Vulnerable

First, a quick synopsis of how marijuana operates: The body’s endocannabinoid system regulates intercellular communication via cannabinoid receptors in the nervous system and brain. “The endocannabinoid system is the master regulator of homeostasis,” Gregory Gerdeman, assistant professor of biology at Eckerd College, tells Yahoo Beauty. “If our electrical system gets too excited, it dampens it down; if cells are moving sluggishly, it speeds things up.”

When an individual uses marijuana, its THC molecules attach to these cannabinoid receptors, altering their activity and triggering a blissed-out sensation, as well as potential paranoia and anxiety. (CBD molecules, also found in weed, give users a mellow feeling that counteracts the high and are the main source of marijuana’s medicinal benefits.)

Cannabinoids are intimately involved in the growth and development of the brain, guiding the wiring of the neural network. And just as a house under construction is not as solid as a completed building, the teen brain is more sensitive than its adult counterpart.

“In this period of critical neural vulnerability, exposure to things like THC can change the trajectory of how the brain develops over time,” Staci Gruber, director of the Cognitive and Clinical Neuroimaging Core at McLean Hospital in Belmont, Mass., tells Yahoo Beauty. Or, as NIDA director Nora Volkow, MD, puts it, the fully grown-up brain has a degree of resiliency that younger brains lack, so “marijuana may have unique, negative effects that may not be present in an adult.”

Does Marijuana Make Teens Dumber?

The pothead slacker spacing out in class is a common stereotype. And evidence does suggest that herb might diminish intellectual capacity. “When individuals smoke marijuana, we see changes within the prefrontal cortex, which is a critical part of the brain right behind your eyebrows, responsible for things like decision making, consciousness, and abstract reasoning,” Gruber says.

During adolescence, the brain eliminates unneeded neurons so that it can operate more efficiently, in a process called synaptic pruning. “When a child is born, he or she has many more neurons than an adult brain,” Volkow says. “It’s almost like a sculpture, where the artist chips away at the stone until it [forms the desired] shape. [The brain] gets rid of some neurons and creates connections that maximize the functions that a particular child is going to need in order to be successful as an adult.”

Marijuana disrupts glutamate receptors, neurotransmitters involved in synaptic pruning; as a result, extraneous neurons may not be effectively phased out and can drag down our cognitive capacity, affecting everything from memory to executive control.

Volkow likens it to the operation of an airport. “The more connections you have, the more communication there’s going to be from one place to another. But too many connections clog the system,” she says. “Of course, too few connections also interfere with your ability to transfer people place to place — and studies have shown that people who consume large quantities of marijuana during adolescence have far fewer connections into the hippocampus, which is one of the main brain regions involved with memory and learning.”

In particular, says John Kelly, MD, professor of psychiatry in addiction medicine at Harvard Medical School and director of the Recovery Research Institute, “it can impact memory consolidation, which is the encoding of short-term information into long-term memories. We learn by contextualizing new information and relating it to other memories in our memory bank. If the information hasn’t been properly encoded, we won’t be able to draw upon it as a resource.”

Marijuana can also decrease myelin, a protective coating around axons of neurons that increases the speed at which electrochemical impulses travel in the brain. “If you don’t have enough myelin, you may be scatterbrained and suffer from attention problems,” Kelly says. “Basically, you’re on the slow train.”

study from Northwestern Medicine found that young adults who smoked marijuana daily for about three years as teens had an abnormally shaped hippocampus and performed poorly on long-term-memory tasks — two years after they stopped using the drug. Compared with a control group, they scored 18 percent worse on a test of memory processes used for daily problem solving and to sustain friendships. And research out of Duke University linked long-term marijuana use before age 18 to a lasting drop in IQ. At age 38, subjects scored an average of eight points lower compared with their results when they were 13 years old.

Yet Gerdeman cautions against jumping to conclusions. “The human brain is a plastic structure that undergoes small morphological changes with time, learning, experience, stress, trauma, meditation, exercise, medication, and yes, cannabis,” he says. “I’m not going to tell you there is no reason to be concerned, but these findings should be viewed with nuance.” He points out that some studies portray a cautionary tale based on brain imaging without showing a corresponding functional deficit, while others fail to control for influential variables like binge drinking.

Can It Stunt Emotional Maturity?

It’s not only intellect that bears the brunt of ganja use at a young age. Research suggests that pot can affect EQ, or emotional intelligence, as much as IQ, thanks to the fact that heavy users have trouble pulling up memories that can inform current decision making. When navigating a relationship or social interaction, “your prefrontal cortex will scan the rest of the brain to see if you have been exposed in the past to a similar situation that can guide you or predict what’s going to happen,” Volkov says. And if someone doesn’t have ready access to that feedback, he or she is at a disadvantage.

What’s more, brain-imaging research has shown that THC targets the prefrontal cortex, the area associated with emotional regulation and social skills. “The prefrontal cortex is the brain’s brake system; it triggers us to look before we leap,” Kelly says. “Inadequate synaptic pruning in this region can increase impulsivity and disinhibition.” When a person’s prefrontal cortex isn’t operating at its optimal level, he or she might react inappropriately, from losing his or her temper at a friend to engaging in unprotected sex.

On the other hand, research from the University of Kentucky, Lexington supports Elliott’s experience: Lonely teens who hit herb had higher levels of self-worth, better mental health, and a lower risk of depression than those who abstained.

Can Weed Make Teens Crazy?

It may reek of reefer madness, but some of the most alarming research points at a link between marijuana use and psychosis. According to a recent paper published in the journal Biological Psychiatry, daily pot use in teens can increase the risk of psychosis from 1 percent to 3 percent. And a study in the American Journal of Psychiatry found that for each year that adolescent males engaged in regular marijuana use, their chances of experiencing psychotic symptoms surged by 21 percent, even a year after they’d stopped using the drug.

“Some people may have a genetic propensity for mental illness like schizophrenia that only manifests under certain conditions,” Kelly says. “In these individuals, chronic exposure to THC over time might trigger a switch that turns on the genes that promote psychosis.”

Again, there’s debate about whether weed is truly at fault. A Harvard study failed to find a causal link between schizophrenia and cannabis use, suggesting instead that family history was the deciding factor; and a review in the journal Schizophrenia Research revealed that although cannabis use is increasing in the U.K., rates of schizophrenia and psychosis are falling. There’s also the chicken-and-egg question — people prone to psychiatric disorders might be more likely to turn to substances in the first place.

Although the matter is still up for debate, Gerdeman has found that “teens with preexisting signs of psychotic tendencies or genetic predispositions who go on to use cannabis heavily are at a greater risk of developing schizophrenia.”

Is It Addictive or Not?

While it’s true that pot’s got nothing on harder drugs like heroin and cocaine, some people do get hooked — and the risk is greater for teens. “Approximately 9 percent of individuals who are exposed to marijuana will become addicted, but if you take marijuana as a teenager, it goes up to 19 percent,” Volkov says. “And 50 percent of teens that use marijuana on a daily basis will become addicted.”

Marijuana activates a part of the brain called the nucleus accumbens, which is a key player in the brain’s reward circuitry, and this can lead to a dependency. “The earlier a person’s brain is exposed to chemical substances, the likelier it is to become sensitized to them,” Kelly says. “When you prime the pump during adolescence, the neurons become adapted to the drug and are altered in such a way that they start to expect its presence.”

The Bottom Line

While the jury is out on how harmful marijuana actually is for adolescents, the majority of researchers agree that the two biggest risk factors are the age of the onset of use and the frequency of use. Basically, the younger someone starts burning one down and the more often they get blazed, the greater the potential harm in terms of brain damage, mental illness, and addiction. As Gruber says, the message for teens should be, “Just say no for now. It’s worth the wait.”

As for Elliott and Liz, they both report that they’re doing well, although their relationship with weed is very different. Elliott, now a host at a high-end restaurant, still wakes and bakes. “I could quit any day if I wanted to, but I don’t want to,” he says. “Parents are so hard on their kids about it, but it’s not a terrible thing.”

Liz, on the other hand, has steered clear of marijuana since rehab and is focused on graduating from high school. “That’s a really big thing that I never thought I would do,” she says. “I’m thrilled about my future … and I have more faith in myself … and can advocate for myself in ways I couldn’t before. … I don’t need to use marijuana in order to be the person that I want to be. I can just be that person authentically.”

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