Marijuana (MJ) use and major depressive disorder (MDD) have additive adverse associations with verbal recall and cortical thickness in the middle temporal gyrus, suggesting that MJ use among those with MDD may be contraindicated, according to a recent study. Young adults (n=141) aged 18-25 years with MJ use and no lifetime MDD (MJ, n=46), MDD and no MJ use (MDD, n=23), MJ use and lifetime MDD (MDD+MJ, n=24), and healthy controls without MDD or MJ use (CON, n=48) were enrolled. Participants completed the California Verbal Learning Test, Second Edition (CVLT-II), a measure of verbal learning and memory. A sub-sample of 82 participants also underwent a structural magnetic resonance imaging (MRI) scan. Group differences in CVLT-II performance, cortical thickness, and hippocampal volume were assessed. Researchers found:
- There was an additive effect of MDD and MJ on memory recall.
- Only MDD, but not MJ, was associated with poorer initial learning, fewer words recalled, more intrusion errors, and lower percent retention.
- There was also an additive effect of MDD and MJ use on reduced cortical thickness in the middle temporal gyrus.
Radoman M, Hoeppner SS. Schuster RM, Evins AE, Gilman JM. Marijuana use and major depressive disorder are additively associated with reduced verbal learning and altered cortical thickness. [Published online ahead of print February 26, 2019]. Cogn Affect Behav Neurosci. doi:10.3758/s13415-019-00704-4.
This paper by Radoman et al. adds to the data that cannabis use may not be good if used by those with psychiatric disorders or propensity towards them. Here, depression as a state seemed to inhibit new learning which makes sense as a cardinal symptom includes poor concentration. In those depressives who also used marijuana, there was a more marked reduction in memory recall, further compounding cognitive status. These subjects also had greater loss of cortical brain tissue. Increasingly, governing bodies are allowing greater access to medical marijuana even for psychiatric disorder treatment where there is often little controlled evidence to support its benefit and ongoing findings that in certain patients it may contribute to, exacerbate, or trigger psychiatric symptoms often in patients’ comorbidities. Per this study, use is also associated with neuronal loss. These findings should be taken from a point of view of association relative to causation of course. Over time, it will be interesting to see if greater access to cannabis, medically, will lower the prevalence of psychiatric symptom suffering as it’s purported to do verses actually increasing prevalence rates of DSM-5 disorders such as major depressive disorder, schizophrenia, etc. It would be ideal if legalization and its profitability was paired with ongoing required study related to population health findings. —Thomas L. Schwartz, MD; Senior Associate Dean of Education, Interim Chair/Professor of Psychiatry, SUNY Upstate Medical University.