Marijuana Poses Risks to Teenagers’ Brains

Adolescents who use marijuana run the risk of lasting effects on their brains and dependency. Drug use may also trigger underlying vulnerability to mental illness.

Teen drug use dropped recently, with many teens spending most of their time at home — but now that they’re out again, the statistics may rise. Nearly 13 percent of all 12- to 17-year-olds reported using marijuana during the past year, along with more than 35 percent of 12th graders, most of them by vaping.

Is it safe? Not as safe as teens probably think.

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Is marijuana addictive?

The answer may be linked to age. If you start using pot as an adult, you have less reason to worry about marijuana’s effect on you than teenagers do.

Research shows that within a year of first trying pot, 11 percent of users ages 12 to 17 had become dependent on it and, within three years, 20 percent had a problem. Those are higher figures than researchers see among people ages 18 to 25.

This might be because the people with a predisposition to addiction tried the drug earlier. Another explanation could be that the drug has a stronger effect on the brain when it is still developing, hard-wiring links between the drug and memories of pleasure.

Does marijuana cause psychosis?

It doesn’t necessarily cause schizophrenia, but teens who are vulnerable to psychosis may be pushed over the edge by cannabis. About 3 percent of heavy users develop schizophrenia.

Does marijuana cause anxiety?

Many teens seem to use pot to reduce anxiety. In a study of more than 1,600 Australian girls recruited at ages 14 and 15, researchers concluded that those who smoked daily were five times more likely to report depression or anxiety over the next seven years. Weekly use doubled the risk. Scientists have hypothesized that some teens use the drug for mood management, but the strategy backfires.

Can marijuana damage the brain?

Some research shows that regular pot use can affect the parts of the brain that are necessary for learning, reason, and focus.

One small study evaluated teens who had sought help for their pot use and underwent brain scans, which revealed differences compared to a group of controls who didn’t use pot. Those differences predicted how much pot they smoked over the next 18 months. The more they smoked, the lower their IQ scores.

One study published in the prestigious Proceedings of the National Academy of Sciences also suggests that chronic users who start as early as age 14 may literally damage their brains.

Using multiple MRI techniques, researchers at the Center for BrainHealth at the University of Texas found that people who started smoking marijuana as early as age 14 had less brain volume in their orbitofrontal cortex, a part of the brain associated with addiction.

Again, using more pot was linked to lower IQ scores, although the scientists couldn’t prove that pot was the cause.

This research team discovered evidence that chronic marijuana usage may trigger a complex “rewiring” of neurons (brain cells that process and transmit information) to compensate for the loss of the orbitofrontal cortex’s gray matter volume. “Eventually, however, the structural connectivity or ‘wiring’ of the brain starts degrading with prolonged marijuana use,” said Sina Aslan, PhD, co-author of the paper and a Center for BrainHealth neuroimaging expert.

“While our study does not conclusively address whether any or all of the brain changes are a direct consequence of marijuana use, these effects do suggest that these changes are related to age of onset and duration of use,” said Francesca Filbey, PhD, director of the Center for BrainHealth’s Cognitive Neuroscience Research in Addictive Disorders.

Does the damage last into adulthood?

Two large longitudinal studies suggest that smoking marijuana impairs mental functioning over time. Among nearly 3,000 people recruited between the ages of 18 to 30 and tested 25 years later, the more years you had smoked, the worse you scored on a vocabulary test, even after the team removed effects of other drug and alcohol use and depression.

In another study, researchers followed more than 1,000 babies born in 1972 and 1973 until they turned 38. They were tested at 13 and again at 38. Those who began smoking regularly as teens lost six to eight points on an IQ test, even if they stopped smoking as adults.

On the other hand, a study with twins tested at ages 9 to12 and again at ages 17 to 20 concluded that if one twin smoked pot and the other didn’t, the pot didn’t lower IQ scores. The authors suggested that some other factor — for example, lack of parental encouragement — might explain both the pot-smoking and lower scores over time.

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