Currently, marijuana is being promoted across the US; however, ever-increasing evidence is accumulating in regard to its harmful effects. A new study has found that teens who were heavy marijuana users (i.e., smoking it daily for about three years) had abnormal changes in their brain structures related to memory. Researchers at Northwestern University Feinberg School of Medicine published their findings online on December 16 in the journal Schizophrenia Bulletin.
The Northwestern researchers have been studying changes in brain structure from marijuana use over the past decade and have found that these changes in brain structure may lead to changes in the way the brain functions. The study group comprised of 67 former marijuana users who had begun smoking marijuana when they were 16 to 17 years old; however, they had not used the drug for an average of two years when they were enrolled in the study. The subjects, who were now in their early twenties, underwent magnetic resonance imaging (MRI) to analyze the brains. The investigators found that memory-related structures in their brains had shrink and collapsed inward; this, was possibly due to a loss of neurons (brain cells). These brain abnormalities appeared to be similar to schizophrenia-related brain abnormalities and correlated with a poor working memory performance. Working memory is the ability to remember and process information in the moment. If necessary, this information can be transferred to long-term memory.
The researchers note that their study is the first study to examine key brain areas in the deep subcortical gray matter of chronic marijuana users with MRI and to correlate abnormalities in these regions with an impaired working memory. Previous studies have evaluated the effects of marijuana on the cortex; however, only a handful of these studies directly compared chronic marijuana use in otherwise healthy individuals and individuals with schizophrenia. The Northwestern investigators found that the younger the individuals were when they started chronically using marijuana, the greater the degree of brain abnormality. They noted that their findings suggest that these brain areas related to memory may be more susceptible to the effects of marijuana if abuse starts at an earlier age.
The study found that chronic marijuana use may contribute to changes in brain structure that are associated with having schizophrenia. Of the 67 subjects, 15 had schizophrenia; 90% started heavy marijuana use before they developed the mental disorder. The investigators note that previous research has reported a connection between marijuana abuse and the development of schizophrenia.