Study: Marijuana Can Affect Teen Brains, No Matter the Amount

The study shows evidence of structural brain and cognitive effects with just one or two instances of cannabis use in adolescence.

Study: Marijuana Can Affect Teen Brains, No Matter the Amount

As many as 32.6 percent of tenth graders in the U.S. reported using marijuana at least once during their lifetime.

A recent study found that teenagers who used recreational marijuana as little as one or two times could see changes in their brain.

The study, which was published Monday in the Journal of Neuroscience, looked at 46 14-year-olds who showed increased volume on MRI scans in parts of the brain involved in emotion-related processing, learning and forming opinions.

Hugh Garavan, the lead author of the study, says he and his team were curious to investigate the popular assumption that one or two joints would have no impact, reports NBC News.

“We were curious to study this and especially to investigate if first uses may actually produce brain changes that affect future behavior like subsequent use,” he said.

Garavan is a professor of psychiatry and the University of Vermont School of Medicine.

Researchers believe that the enlargement of gray matter seen in the brain scans of the teens suggests a disruption in normal adolescent development.

“One possibility is that the cannabis use has disrupted this pruning process, resulting in larger volumes (i.e., disruption of typical maturation) in the cannabis users,” Garavan said. “Another possibility is that the cannabis use has led to a growth in neurons and in the connections between them.”

According to the most recent data from the National Institute of Drug Abuse, 32.6 percent of tenth graders reported using marijuana at least once during their lifetime.

The institute says risks of marijuana use include reduced school performance, reduced life satisfaction, impaired driving and use of other drugs.

These studies come at a time where marijuana is now legal in 10 states and more are expected to follow.

Teens are also using e-cigarette products to smoke marijuana, according to this study. Students who participated reported using e-cigarettes to vaporize hash oil, marijuana leaves and wax infused with THC.

E-cigarettes have been the most commonly used tobacco product among middle and high school students since 2014, according to the CDC. Recent data showed there was a 78 percent increase in youth vaping between 2017 and 2018.

The FDA has cracked down on e-cigarette companies like Juul and is considering banning flavored products form the market, as they can be more appealing to teens.

According to another study published on Monday medical journal Pediatrics, teens who live in areas with strong regulations could be at lower risk of tobacco use, reports CNN.

“We found that youth living in areas with strong licensing requirements were less likely to begin using e-cigarettes and cigarettes during the one-and-a-half-year follow-up, on average, compared to youth who resided in areas with weaker regulations,” said Rober Urman, an author of the study.

Researchers say more work is needed to find solid evidence about the enlargement of gray matter and the negative effects on the brain.

Garavan and his team plan to investigate the effects of alcohol and other psychoactive substances as well.

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About the Author


Katie Malafronte is Campus Safety's Web Editor. She graduated from the University of Rhode Island in 2017 with a Bachelor's Degree in Communication Studies and a minor in Writing & Rhetoric. Katie has been CS's Web Editor since 2018.

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One response to “Study: Marijuana Can Affect Teen Brains, No Matter the Amount”

  1. James Tripp says:

    Increase in Grey matter

    Senior author and University of Vermont (UVM) Professor of Psychiatry Hugh Garavan, Ph.D., and first author and former UVM postdoctoral fellow Catherine Orr, Ph.D., say this research is the first to find evidence that an increase in gray matter volume in certain parts of the adolescent brain is a likely consequence of low-level marijuana use.

    Decrease in Grey matter;

    These results suggests that small GM volumes in the medial temporal lobe are a risk factor for heavy cannabis use or that the effect of cannabis on GM reductions is limited to adolescence with no further damage of continued use after early adulthood.

    The results showed that compared with controls, marijuana users had significantly less bilateral orbitofrontal gyri volume, higher functional connectivity in the orbitofrontal cortex (OFC) network, and higher structural connectivity in tracts that innervate the OFC (forceps minor) as measured by fractional anisotropy (FA).

    So which is it? Increase or decrease?

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