MedicalResearch.com Interview with:
Dr. Nicole Karcher, PhD
Post-doctoral scholar with the NIMH Training in Clinical Sciences fellowship
Department of Psychiatry
Washington University School of Medicine
MedicalResearch.com: What is the background for this study? What are the main findings?
Response: For over fifteen years, researchers have debated the role that cannabis use plays in the development of both psychotic disorders as well as subthreshold psychotic symptoms, such as psychotic-like experiences (PLEs). There is still a lack of consensus regarding the nature of the association between cannabis use and psychosis risk, with some research finding evidence for genetic overlap, while other research finds evidence for potentially causal pathways.
The current study examined data from twins and siblings from two different samples, the U.S.-based Human Connectome Project and the Australian Twin Registry, with a total of 4,674 participants. Overall, psychotic-like experiences were associated with three separate cannabis use variables [frequent (≥100 times) use, a Cannabis Use Disorder diagnosis, and current cannabis use]. Furthermore, the current research found evidence for both shared genetic and individual-specific contributions to the association between PLEs and these three cannabis use variables. More specifically, while the association between cannabis use and psychotic-like experiences was largely attributable to shared genetic factors, cannabis users were more likely to endorse PLEs in comparison to the relative who used cannabis less.
MedicalResearch.com: What should readers take away from your report?
Response: Overall, the current study helps clarify the association between cannabis use and psychotic-like experiences. While genetic overlap was a major contribution to this association, there was still evidence for person-specific influences that may be causal in nature. These results suggest that targeting cannabis use prevention may be an important tool in preventing worsening of PLEs in individuals at increased genetic liability to psychotic-like experiences and cannabis use.
MedicalResearch.com: What recommendations do you have for future research as a result of this work?
Response: It will be important for future research to clarify the direction of individual-specific factors (ie, whether increased cannabis use leads to PLEs or increased psychotic-like experiences lead to cannabis use). Thus, research should examine the association between cannabis use and PLEs over time, assessing PLEs prior to the initiation of cannabis use. It will also be important for future research to account for varieties of cannabis, as there is some evidence that while THC is associated with psychosis risk, cannabidiol (CBD) has been associated with antipsychotic properties.
We would like to thank all the participants that contributed to this study.
Karcher NR, Barch DM, Demers CH, et al. Genetic Predisposition vs Individual-Specific Processes in the Association Between Psychotic-like Experiences and Cannabis Use. JAMA Psychiatry. Published online October 17, 2018. doi:10.1001/jamapsychiatry.2018.2546
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