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Cannabis Abuse DOES Cause Long-term Brain Damage in Young Adults

It has been a long held and widely spread belief that the effects of marijuana use are short-term. Chronic pot-users are described as dull or slow, but many clinicians believe that such effects will wear off. We have heard estimates that within three months most effects will be neutralized, but altogether in 12 months. Cognitive issues related to cannabis abuse include impairments in learning, memory, attention and processing speed. A common pattern that is noted on intelligence tests such as the Wechsler Intelligence Scale for Children (WISC), is that verbal and visual intelligence indexes appear much higher than the index scores for working memory and processing speed. New research also points to impairments in executive functioning including decision making and problem solving.

In a new article published in the Journal of Neuroscience (April, 2014), researchers from Harvard and Northwestern Universities challenge common wisdom by stating there is a strong correlation of: casual marijuana use and major anatomical changes in the brain. In brief, the researchers evaluated 40 young adults (18-25), half of which reported they were "casual" users of cannabis, the other half were age and gender matched non-users. Sophisticated quantitative neuro-imaging techniques were used and "the scientists found that the more the marijuana users reported consuming, the greater the abnormalities in the nucleus accumbens and amygdala. The shape and density of both of these regions also differed between marijuana users and non-users."

According to the researchers, "the degree of abnormalities is increased by the number of joints you smoke in a week." Analysis found correlative evidence that long-term damage occurs in the nucleus acumbens and amygdala of even "recreational" users. While correlation is not causation, these findings have significant meaning and open the door for increased research using fMRI and neuropsychological testing to evaluate functional changes.  

Recent Media Coverage:

·         Society for Neuroscience (Press Release)
·         Marijuana News: Casual Pot Use Impacts Brains of Young Adults, Researchers Find (The Oregonian)
·         Study Finds Brain Changes in Young Marijuana Users (Boston Globe)
·         Casual Marijuana Use Linked to Brain Changes (USA Today)
·         Even Casually Smoking Marijuana Can Change Your Brain, Study Says (Washington Post)
·         Study Finds Changes in Pot Smokers' Brains (Denver Post)
·         Recreational Pot Use Harmful to Young People's Brains (TIME)



Gilman, JM et al. (2014). Cannabis use is quantitatively associated with nucleus acumbens and amygdala abnormalities in young adult recreational users. The Journal of Neuroscience, March, 2014.

Meier, M. et al. (2012). Persistent cannabis users to show neuropsychological decline from childhood to midlife. Proceedings of the National Academy of Sciences, April, 2012.





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