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How marijuana may affect your child’s brain—and future

The brain is a complex organ that plays a role in everything from the actions a person chooses to take to how she solves problems to how she creates memories. And marijuana can impact your child’s brain—and the actions, decisions, and learning that affect her future—in many ways. This is especially true during the teen years, when your child’s brain is still developing and is more vulnerable to the effects of drugs and alcohol.1

Scientists are learning more all the time about marijuana’s effects on the brain. There is now a large body of evidence—including several studies that have tracked people from all around the world throughout many years of their lives—showing that early (before age 18), frequent, and continuous marijuana use may have significantly negative impacts on the brain. And those negative impacts on the brain may lead to negative impacts on a person’s life, including mental health issues and lower education and job prospects.

THC: A chemical that disrupts the brain’s normal functioning

The main psychoactive chemical in marijuana that causes the feeling of being “high” is called delta 9-tetrahydrocannabinol (or THC). When your child uses marijuana, the THC moves through his bloodstream to organs throughout his body—including his brain. Here, it attaches to receptors (called cannabinoid receptors) on certain neurons (the nerve cells that work to send and receive messages from the brain to other parts of the body) and disrupts their normal functioning.2

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Marijuana may cause changes in the brain.

Frontal Cortex: The part of the brain that regulates many important functions, including complex thinking, personality, behavior, and judgment.3

A study of more than 1,000 residents of a New Zealand city who were followed from birth to age 38 found that those who began using marijuana in adolescence and continued using it persistently experienced a decline in brain function. This decline was independent of the participants’ years of education or recent drug or alcohol use. The greatest declines were observed in processing speed and executive function—which includes processes such as the ability to control one’s attention and inhibitions as well as the ability to reason and problem solve.

White Matter: Bundles of nerve fibers found in the deeper tissue of the brain that help the neurons in your child's brain communicate.4

Studies have shown evidence of poorer integrity in the white matter tissue of teens who use marijuana—and especially those who also drink alcohol. Scientists believe that white matter integrity is important for efficient connectivity in the cortex of the developing brain.

How this may impact your child’s life:
The brain changes that occur from using marijuana may make your child less inhibited and more impulsive—and therefore more likely to take dangerous risks (like driving while drunk or high).5

In fact, two studies showed that poorer white matter integrity in teens who used marijuana and drank alcohol were linked to problems with attention, working memory, processing speed, emotional functioning, and prospective risk taking. And heavy marijuana use is linked to an increased risk for motor vehicle crashes.6

Marijuana may cause changes in the brain.7

Frontal Cortex: The part of the brain that is involved in higher-order functioning including problem-solving, intelligence, and concentration.

A study of 1,037 residents of Dunedin, New Zealand who were followed from birth to age 38 found that those who began using marijuana in adolescence and continued using it persistently experienced a decline in brain function—even after controlling for years of education and ruling out factors such as marijuana use within the past day or week and dependency on other drugs, including alcohol. The greatest impairments were found in the areas of executive functioning and processing speed. And functioning was not fully restored even after quitting marijuana for those who’d started using marijuana during adolescence.

Third party observers (such as friends and family members) also reported greater memory and attention problems among those participants who had started using marijuana during adolescence.

Hippocampus: The part of the brain responsible for helping your child learn and remember new information.

In one study in which researchers used MRI imaging to map the brains of 97 subjects, significant differences in the shape of the hippocampus were found in subjects who had been diagnosed in the past with marijuana use disorder (but did not have a current diagnosis of the disorder) as compared to those who had never been diagnosed with any substance use disorder. These differences were linked to deficits in episodic memory (a person’s memory of their unique past personal events and the context surrounding those events).

How this may impact your child’s life:
Heavy marijuana use during adolescence can cause problems with attention, learning, memory, and the ability to quickly process information.8 That may a factor in why marijuana use in teens has been linked to lower academic performance and worse job prospects.9

In fact, a study of 2,290 Australian young adults interviewed at age 20 found that those who had started using marijuana in early adolescence (age 14 years or younger) were nearly 21% less likely to have graduated from high school. Among students who did complete high school, those who began using marijuana in early adolescence and used it at high intensity scored approximately 5% lower on university entrance exams.

Heavy marijuana users also experience attention and memory problems that last beyond the time when they are high—and can worsen with years of regular use.10

In fact, continued regular use of marijuana has been shown to lead to a decrease in IQ 20 years later.11

A study of 962 residents of Christchurch, New Zealand studied over the course of 35 years showed that those who used marijuana before age 15 had worse educational and economic outcomes than those who did not use marijuana before the age of 18. The difference in outcomes was independent of other factors in the individuals’ backgrounds (such as childhood trauma or early academic achievement). In addition, increased use of marijuana between ages 15-21 was linked to an increased risk of both welfare dependence and unemployment at 21-25 years of age. And those who reported using marijuana on 400 or more occasions were almost 5X more likely to be welfare dependent and more than 3X more likely to be unemployed than those who did not use marijuana.

Marijuana may cause changes in the brain.

Limbic system: The brain’s “reward circuit”—a network of structures within the brain that regulate your child’s ability to feel pleasure and can trigger her body’s need to continue experiencing that feeling of pleasure. These structures include the hippocampus (regulates memory), the amygdala (regulates emotion), the nucleus accumbens (regulates motivation and reward), and others.12

In a recent study examining the MRI scans of young adult (18-25 years of age) marijuana users vs. nonusers, abnormalities in gray matter density, volume, and shape were observed in the nucleus accumbens and amygdala of marijuana users—even after controlling for age, sex, alcohol use, and cigarette smoking—and the degree of abnormality increased with higher usage. In addition, fundamental relationships observed among structural measures of control in nonusers were absent in users. This suggests a possible link between marijuana use and a disruption of neural organization in specific regions of the nucleus accumbens and amygdala.

How this may impact your child’s life:
Addiction can change your child’s brain in a way that leads him to continue to use drugs even if the use of those drugs causes harm to his health or relationships.13

A summary of studies showed that about 10% of people who ever use marijuana—and up to 50% of those who use it daily—will become dependent on marijuana and continue to use it despite experiencing problems.

No one can predict who will become addicted to marijuana or other drugs and who won’t. But research has established that marijuana is addictive—and that the earlier a person starts using it, the more likely it is that she will develop a chemical dependence. In fact, teens who smoke marijuana are 3X more likely to become dependent than adults.14 And about 1 in 6 teens who start using marijuana before age 14 become addicted.15

Marijuana may cause changes in the brain.

Amygdala: The part of your child’s brain that regulates emotions, including anxiety and fear.16

A recent study showed that endocannabinoid signaling plays a prominent role in modulating the neuron circuitry of the central amygdala that helps to regulate stress response and emotional learning.

How this may impact your child’s life:
Scientists are still studying marijuana’s impact on anxiety, but there is a fair amount of evidence that non-medical marijuana use can worsen anxiety. Studies have shown that early and persistent marijuana use, in particular, can lead to the development of anxiety disorders later in life. In fact, one study showed that regular marijuana use or a diagnosis of marijuana dependence during adolescence was significantly associated with a greater risk of anxiety disorders in adolescence and late young adulthood (defined as up to age 29)—even among those who had stopped using marijuana.

In other research, using marijuana weekly or more often has also been associated with doubling a teen's risk for depression or anxiety.18 A study of 962 residents of Christchurch, New Zealand who were followed from birth to age 35 showed a modest link between marijuana use and major depression. Data from the study also suggests that earlier and heavier marijuana use among males strongly increases the risk of suicidal thoughts.

Marijuana may cause changes in the brain.19

Cerebellum: The part of your child’s brain that controls balance and coordination.

Basal Ganglia: The part of your child’s brain that helps regulate her ability to plan and control movements.

How this may impact your child’s life:
Marijuana can impair your child’s coordination and slow her reaction time—and this can affect her ability to perform activities such as driving a car.20 In fact, heavy marijuana use is linked to an increased risk for motor vehicle crashes.21

IS MY CHILD AT RISK?

Sometimes risk factors are not obvious.

 

MONITOR YOUR TEEN

Constant monitoring of your teen can seem overwhelming. Instead, identify a few areas of concern listed below and download or print out a checklist of practical and useful tips you can use to help your teen.

 

SET THE FOUNDATION

The Search Institute has identified 40 skills, experiences, relationships, and behaviors (called developmental assets) that help set the foundation for teens to grow into happy and healthy adults with much to contribute to the world. Create a custom checklist of the areas where you may be able to help your child build these assets.