Heavy marijuana abuse linked to abnormal brain structure and poor memory

Washington – Researchers have said teens who were heavy marijuana users – smoking it daily for about three years – had abnormal changes in their brain structures related to working memory and performed poorly on memory tasks.

The brain abnormalities and memory problems were observed during the individuals’ early twenties, two years after they stopped smoking marijuana, which could indicate the long-term effects of chronic use.
Memory-related structures in their brains appeared to shrink and collapse inward, possibly reflecting a decrease in neurons.

The study also shows the marijuana-related brain abnormalities are correlated with a poor working memory performance and look similar to schizophrenia-related brain abnormalities.

The younger the individuals were when they started chronically using marijuana, the more abnormally their brain regions were shaped, the study reports.

The findings suggest that these regions related to memory may be more susceptible to the effects of the drug if abuse starts at an earlier age.

lead study author Matthew Smith, an assistant research professor in psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine, said that the study links the chronic use of marijuana to these concerning brain abnormalities that appear to last for at least a few years after people stop using it.

The groups in the study started using marijuana daily between 16 to 17 years of age for about three years. At the time of the study, they had been marijuana free for about two years. A total of 97 subjects participated, including matched groups of healthy controls, subjects with a marijuana use disorder, schizophrenia subjects with no history of substance use disorders, and schizophrenia subjects with a marijuana use disorder.

The paper is set to be published in the journal Schizophrenia Bulletin.