A girl, lying in bed, smoking marijuanaJust how does marijuana use affect a developing teenager’s brain? Researchers, lead by Matthew Smith, at Northwestern University Feinberg School of Medicine have some answers. Smith and his team compared brain images of young adults who had used marijuana as teenagers with non-marijuana smoking young people as well as people diagnosed with schizophrenia. They discovered that marijuana use during the teenage years is linked with brain abnormalities that resemble those present in schizophrenia. These findings may illuminate some of the risks associated with marijuana abuse in young people.

There were a total of 97 subjects involved in the study, divided into four groups: healthy controls who did not have a history of marijuana usage, subjects with a history of cannabis use disorder, subjects with a history of cannabis use and a diagnosis of schizophrenia, and subjects diagnosed with schizophrenia, but who had not used marijuana. The participants were in their 20s, but the marijuana-using groups had begun their history with the drug at the age of 16 or 17. They had been marijuana-free for approximately two years at the time of the study.

The researchers used MRI scans to examine three brain regions that are critical to motivation and working memory: the striatum, the thalamus, and the globus pallidus. In addition to the MRIs, the participants also did four tests of working memory.

The findings indicate a resemblance in the targeted brain regions between the marijuana users and the subjects with schizophrenia. The affected regions appeared smaller than those of the control subjects, possibly due to a decrease in neurons; the subjects who started using at the youngest ages were the most affected. The heavy users also performed worse on the memory tests than both the controls and the non-using group of schizophrenics. Additionally, 90% of the users who had schizophrenia reported that they developed the disorder after they started using marijuana.

Although the results do not suggest a direct or certain cause-and-effect relationship between marijuana use and these specific brain abnormalities, they do seem to indicate that the effects of marijuana use are longer lasting that some might suspect. The authors call for more research to fully understand how chronic marijuana use affects teens.

This research is published in the journal Schizophrenia Bulletin.

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