Two studies that came out today in the Journal of American Medical Association explored the effects of marijuana in the developing brain. Each yielded mixed results, but one thing is clear: there is no evidence to suggest that smoking pot causes brain damage in young adults.
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Twins with discordant marijuana use show no difference in their brain volumes
Researchers interviewed and conducted neuroimaging on young adult twins or siblings with different marijuana use habits. Studies in twins or siblings allow controlling for genetic and familial factors on brain growth. Of the pool of participants, 71 twin pairs had never used marijuana, 81 pairs used it casually, and 89 pairs were comprised of one sibling who used it and one who did not. The neuroimaging analysis looked at the amygdala and the right ventral striatum⎯areas related to emotions and reward. They found that brains of casual marijuana users had smaller amygdala and right ventral striatum than the brains of siblings who never used marijuana, with the difference being within the bounds of normal variation. What is interesting is that even those who had never used marijuana had smaller amygdala if their sibling used marijuana. This means that marijuana does not cause lower amygdala volumes. Instead, common genetic and environmental factors (that siblings experience) predispose young adults to both marijuana use and smaller amygdala in their brains.
Males with a high risk for schizophrenia are more susceptible to the brain-altering effects of marijuana
In another study, 1574 young adults and adolescents were examined based on their genetic risk for schizophrenia and their marijuana use. They used brain cortical thickness as an indicator of brain maturation and information processing power. While both high-and low-risk females and low-risk males had no changes in their cortical thickness upon marijuana use, high-risk males responded differently. Their brains showed lower cortical thickness when they used marijuana. Thus, males who are at a high risk for schizophrenia show changes in their brain when they use marijuana. This doesn’t mean that the marijuana causes changes in the brain structures, but merely that common precipitating factors could increase the risk of schizophrenia in young men as well as make them vulnerable to marijuana use.
This is not an endorsement for marijuana
While these studies have importantly pointed out the fallacy in assuming causation from correlation, the results are just the tip of the iceberg. More research needs to be conducted to study different areas of the brain to put stock into these findings, and eventually proposing legislative solutions.
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Casual Marijuana Use Doesn"t Shrink Brains
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