Use of Marijuana At Young Age Linked To Functional Brain Abnormalities and Lower IQ Interview with:

Elizabeth Osuch, M.D. Associate Professor; Rea Chair Department of Psychiatry FEMAP--London Health Sciences Centre London, ON

Dr. Elizabeth Osuch

Elizabeth Osuch, M.D.
Associate Professor; Rea Chair
Department of Psychiatry
FEMAP–London Health Sciences Centre
London, ON What is the background for this study? What are the main findings?

Response: As a researcher and psychiatrist doing clinical work in youth aged 16-25 with mood and anxiety disorders I often see patients who are depressed and believe that using marijuana (MJ) improves their mood.  Yet they remain depressed.  This was the clinical inspiration for this brain imaging study, where we investigated emerging adults with Major Depressive Disorder (MDD).  Subject groups included patients with MDD who did and did not use MJ frequently.  Our results showed that the MDD+MJ group did not have significantly less depression than the MDD alone group, and the brain abnormalities found in MDD were not corrected by MJ use in the MDD+MJ group.  In fact, some of the brain differences were worse with the addition of MJ, while others were just different.

We also found that, if we sorted the participant groups by whether or not they had started marijuana use before or after their 17th birthday, there were major abnormalities in functional brain connectivity within the younger onset MJ using group.  In addition, the younger age of onset group had a significantly lower average IQ than the older onset/non  marijuana use group.  This was driven by the Vocabulary Subscale score of the WAIS.  Since this was not a longitudinal study, it was impossible to determine causation for these relationships.

Lastly, we found a significant association between being a carrier of the risk allele of BDNF (Brain Derived Neurotropic Factor) and being an early onset  marijuana user.  Since this was a small study, this will need to be confirmed with more subjects. What should readers take away from your report?

Response: The most important messages were that there was no evidence that  marijuana use corrected the functional brain deficits (or symptoms) associated with MDD; that early onset marijuana use was associated with both functional brain abnormalities and lower IQ; and that the BDNF risk allele may be associated with early onset MJ user. What recommendations do you have for future research as a result of this study?

Response: Future research can involve longitudinal studies that capture brain function and IQ before the use of any  marijuana to help determine causal links between the associations found in this study related to early onset  marijuana use.  Another study could involve a longitudinal investigation of the effects of MJ use on MDD.  And, as mentioned, a larger study of early onset  marijuana users and the association with the BDNF risk allele will need to be conducted. Thank you for your contribution to the community.


A. Osuch, K. Manning, R. A. Hegele, J. Théberge, R. Neufeld, D. Mitchell, P. Williamson, R. C. Gardner.Depression, marijuana use and early-onset marijuana use conferred unique effects on neural connectivity and cognition.Acta Psychiatrica Scandinavica, 2016; DOI:10.1111/acps.12629

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.

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