Young adults with both marijuana use and major depressive disorder showed worse verbal recall and thinner cortex in the middle temporal gyrus compared to those with either condition alone.
Young adults with depression who use marijuana, psychiatrists, and researchers studying substance use in mood disorders.
MDD + marijuana produced the worst verbal memory and cortical thickness
What the researchers found
MDD and marijuana use had additive effects on memory recall and cortical thickness in the middle temporal gyrus. MDD alone (but not marijuana alone) was associated with poorer initial learning, fewer words recalled, more intrusion errors, and lower retention. The combination produced the worst outcomes.
Why it matters
Depression and marijuana use frequently co-occur in young adults. Finding that their effects are additive rather than redundant suggests that marijuana use among people with depression carries an extra cognitive cost.
The numbers in context
141 participants ages 18-25. Additive effects on verbal recall and middle temporal gyrus thickness. MDD alone associated with poorer learning, fewer words recalled, more intrusion errors.
How the study worked
Cross-sectional study of 141 young adults (ages 18-25) in four groups: marijuana only (n=46), MDD only (n=23), MDD + marijuana (n=24), and healthy controls (n=48). Participants completed the California Verbal Learning Test and a subset (n=82) underwent structural MRI.
What this study cannot tell us
Cross-sectional design cannot determine causation. The MDD and MDD+MJ groups were smaller than the other groups. The MRI subsample was 82 of 141 participants.
How to read the evidence
Moderate: well-designed cross-sectional study with neuroimaging, but small group sizes and non-longitudinal design.
When this study was published
Published in 2019.
The bigger picture
Young adults with depression may use marijuana for symptom relief, but this study suggests doing so may compound their cognitive difficulties rather than helping.
Questions still open
- Would marijuana cessation in depressed individuals reverse the additive cognitive effects? Does the severity or frequency of marijuana use modulate the interaction? Are the cortical thickness changes permanent?
Common questions
What does "additive" mean here?
Did marijuana alone affect verbal memory?
Read the original research
Marijuana use and major depressive disorder are additively associated with reduced verbal learning and altered cortical thickness.
Cognitive, affective & behavioral neuroscience, 19(4), 1047-1058
Citation
Radoman, Milena; Hoeppner, Susanne S; Schuster, Randi M; Evins, A Eden; Gilman, Jodi M. (2019). Marijuana use and major depressive disorder are additively associated with reduced verbal learning and altered cortical thickness.. Cognitive, affective & behavioral neuroscience, 19(4), 1047-1058. https://doi.org/10.3758/s13415-019-00704-4
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