A new study from Northwestern University Feinberg School of Medicine (FSM) that used magnetic resonance imaging (MRI) to analyze the brains of 67 former marijuana users revealed that chronic marijuana use was associated with poor growth in the brain’s deep subcortical gray matter; a region linked with memories. The participants had started using marijuana when they were 16 to 17 years old, but at the time of the study, they were all marijuana-free for two years, on average.
Lead study author Matthew Smith, an assistant research professor in psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine said his team found that the brain structures of the marijuana users closely resembled those of schizophrenia patients. This included collapsed memory-related structures, shrinkage of neurons, and deficient processing in the pre-frontal cortex, which controls motivation.
Teens who began using marijuana earlier were found to display greater brain abnormalities than those who started using it later in life, indicating a greater susceptibility to damage in growing brains. The negative effects of the drug (including poor memory) were displayed among teenagers who smoked daily for a period of three years. The study links the chronic use of marijuana to these brain abnormalities that appear to last for at least a few years even after people stop using it. However, further research is required to understand the effect of marijuana on the brain.
"Future longitudinal studies could help determine whether cannabis use contributes to these observed shape differences or whether they are biomarkers of a vulnerability to the effects of cannabis that predate its misuse."