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Teen pot smoking causes adult brain damage

Teresa Tanoos's picture
Study shows teen pot smoking damages brain as adult.

Teenagers who smoke pot are putting themselves at risk for damaging their brain and altering memory and reasoning circuits located in the sub-cortical region of the brain, according to a new study published Monday in the journal Schizophrenia Bulletin.

Researchers from Northwestern University Feinberg School of Medicine in Chicago conducted the study, and the results showed that the brains of adults who had been heavy pot smokers as teens had been altered, causing them to perform worse on memory tests and having less volume in the thalamus of their brains than their non-using healthy counterparts.

Even those who had once been heavy pot smokers, but had not used it for over two years prior to the memory tests, performed poorly, which demonstrates the danger of teenagers smoking pot because they “are at a very vulnerable stage neurodevelopmentally,” according to study leader Matthew Smith.

Smith added that adolescents suffer long-term consequences when they “throw stuff into the brain that’s not supposed to be there.”

The Substance Abuse and Mental Health Services Administration reports that U.S. teenagers between the ages of 12 and 17 who used marijuana during the last month dropped from 12 percent in 2002 to 9.5 percent in 2012, which still means that millions of American teens are smoking pot.

Adding to the problem is the legalization of marijuana in some states, which could potentially give young people greater access to the drug.

So what does teen pot smoking do to their brains as adults?

The answer may surprise those who thought marijuana was a harmless substance and less dangerous than drinking and illicit drugs.

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According to a study published last year in the Proceedings of the National Academy of Sciences (PNAS), adults who used marijuana regularly when they were teenagers still had measurable “neuropsychological decline”, as well as more cognitive problems than non-users did – and that was the case even if the adult had stopped using years before.

For this newest study, researchers recruited a group of adults with an average age of 25 who had a prior history of heavy marijuana use during their teens, although they had stopped using on a regular basis.

Among the adult participants, 10 had a history of mental disorders related to marijuana use, 15 had been diagnosed with schizophrenia after having a history of marijuana use, and 28 had schizophrenia, but did not have a history of regular marijuana use.

The average age of the participants was 25 at the time of testing. For comparison’s sake, the researchers also recruited 44 non-using healthy controls for the study.

The researchers then conducted MRI brain scans on the participants, examining three particular regions of the brain: 1) the striatum, which is associated with reward and motivation; 2) the thalamus, which is the main portion of the brain that controls cognition; and 3) the globus pallidus, which is linked with memory and movement.

The results showed that those who had previously been heavy users of marijuana had brain abnormalities, regardless of whether they also had schizophrenia or not. For example, the thalamus of heavy users had much less volume than the healthy non-users.

Next, the participants took four different tests to measure memory. The tests included having them try to remember a group of numbers they’ve been shown.

Again, the results showed that the heavy marijuana users performed much worse on the memory tests than the healthy non-using controls and non-using schizophrenics, and this was true regardless of whether the heavy user also had schizophrenia.

As Smith explained, they not only saw worse performance in the marijuana using groups, but they also found that the younger the participants started using, the worse they performed on the tests – and the more abnormal their brains were after the MRI scans.

SOURCE: Schizophrenia Bulletin, Cannabis-Related Working Memory Deficits and Associated Subcortical Morphological Differences in Healthy Individuals and Schizophrenia Subjects, published December 15, 2013.