Is Teen Drug Use Related to Brain Size?

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fMRI image of preteen brain

Richard Watts, PhD, University of Vermont and Fair Neuroimaging Lab, Oregon Health and Science University

This blog has discussed how using drugs in your teen years can affect how your brain develops in lots of important ways.

Recently, researchers found another connection: Teens who use nicotine, alcohol, and marijuana (or weed) have two brain areas that are smaller than average when they become adults.

This doesn’t necessarily mean that teen drug use causes those brain areas to be smaller. Other factors could also be involved. But this connection (what scientists call a correlation) is worth knowing about, and is being studied by scientists.

Researchers found that higher levels of alcohol, cigarette, and marijuana use before age 19 correlated with significantly less “gray matter” in two brain areas at age 25.

Less gray matter in a brain area could mean it contains fewer nerve cells (neurons), which might reduce that brain area’s ability to function in a healthy way.

Which areas are affected?  

  • The amygdala, which processes emotions, was smaller in people who reported greater use of those substances at ages 12 to 15.
  • The pars opercularis, in the prefrontal cortex, was smaller in people who reported greater use of the substances at ages 16 to 18. The prefrontal cortex is sometimes called the “CEO of the brain”; it controls your ability make smart decisions.

Having less gray matter in these two brain areas could be either:

  • A cause of substance use (if the teens had less gray matter to begin with, and this made them more likely to use drugs), or…
  • An effect of substance use (if using drugs affected how the two areas grew).

Why could these particular parts of the brain be smaller in teens who use more of certain drugs? Researchers aren’t sure yet, but we do know that the teen brain matures in stages:

  • The amygdala is part of the limbic system, which matures earlier in brain development.
  • The pars opercularis is part of the forebrain circuit that matures later.

This all suggests that as the brain matures in the teen years, it goes through stages, and its development may affect—or be affected by—substance use. We’ll learn more as the research continues.

Learn more: Why are drugs so hard to quit?

Find Help Near You

Use the SAMHSA Treatment Locator to find substance use or other mental health services in your area. If you are in an emergency situation, this toll-free, 24-hour hotline can help you get through this difficult time: call 1-800-273-TALK, or visit the Suicide Prevention Lifeline. We also have step by step guides on what to do to help yourself, a friend or a family member.

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