Cannabis use disorder impaired executive attention in adolescents with schizophrenia but not in healthy adolescents, suggesting cannabis has a selectively harmful effect on attention in the context of psychotic illness.
Read this if you want to understand how cannabis use interacts with schizophrenia to affect cognitive function.
Cannabis impaired attention in schizophrenia but not in healthy adolescents
What the researchers found
Researchers compared attention performance across four groups of adolescents: early-onset schizophrenia with cannabis use disorder (EOS+CUD, n=18), schizophrenia only (EOS, n=34), cannabis use disorder only (CUD, n=29), and healthy controls (n=53). A significant interaction emerged: in the executive attention network, adolescents with both schizophrenia and cannabis use disorder performed worse than those with schizophrenia alone.
However, adolescents with cannabis use disorder alone showed no difference from healthy controls. This selective effect suggests that cannabis has a moderating impact on attention specifically in the context of schizophrenia.
The attention deficit was associated with smaller surface area in the right caudal anterior cingulate cortex, suggesting an anatomical substrate for the cognitive impairment.
Why it matters
Cannabis use is common among people with schizophrenia, and understanding whether it worsens the cognitive deficits of the illness has direct clinical implications. The selective interaction found here suggests cannabis may specifically compound schizophrenia-related cognitive problems.
The numbers in context
134 adolescents across four groups. Significant EOS x CUD interaction in executive attention. Attention deficit correlated with smaller right caudal anterior cingulate cortex surface area in the EOS+CUD group.
How the study worked
Four-group comparison using the Attention Network Test during fMRI in 134 adolescents. 2x2 design crossing EOS status with CUD status. Brain surface area in the anterior cingulate cortex was measured and correlated with attention performance.
What this study cannot tell us
Cross-sectional design. Relatively small group sizes, especially the EOS+CUD group (n=18). Cannot determine whether cannabis caused the attention deficit or whether more severely affected patients were more likely to use cannabis. The results are described as preliminary.
How to read the evidence
Well-designed four-group comparison with brain imaging correlation, though limited by small subgroup sizes and cross-sectional design.
When this study was published
Published in 2014.
The bigger picture
This study adds nuance to the cannabis-psychosis literature by showing that the cognitive effects of cannabis may depend on underlying brain state. Rather than a universal effect, cannabis may be particularly harmful to brain functions already compromised by psychotic illness.
Questions still open
- Does cannabis cessation improve attention in adolescents with schizophrenia? Is the anterior cingulate cortex difference a consequence of cannabis use, schizophrenia, or both? Would these findings replicate in adult schizophrenia populations?
Common questions
Does cannabis make schizophrenia worse?
Did cannabis affect attention in healthy teenagers?
Read the original research
Executive attention impairment in adolescents with schizophrenia who have used cannabis.
Schizophrenia research, 157(1-3), 48-54
Citation
Epstein, Katherine A; Kumra, Sanjiv. (2014). Executive attention impairment in adolescents with schizophrenia who have used cannabis.. Schizophrenia research, 157(1-3), 48-54. https://doi.org/10.1016/j.schres.2014.04.035
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