(Oct. 9, 2018) As we wrote last week, the association between cannabis use, commonly known as marijuana, and serious mental illness is controversial. In that post, we examined research concerning marijuana's applicability as a therapeutic drug. This week's research blog is the second in the two-part series and focuses on questions linking cannabis use with the development of schizophrenia.
There is significant evidence to support the association between heavy marijuana use and an increased risk of developing schizophrenia among adolescents and that it worsens symptoms in individuals who already have the disease. However, the methodology behind such research is observational and not experimental, meaning individuals were not randomized or in a controlled environment and only correlations and associations can be concluded. Opponents of the research continue to give cautions for coming to any conclusions on any causal links between cannabis use and developing schizophrenia.
Given the degree to which marijuana use has become more accepted, if not ubiquitous, in recent years, the implications of inconclusive research connecting cannabis use to developing schizophrenia are becoming increasingly more troublesome. According to the Substance Abuse and Mental Health Services Association, 26 million individuals used marijuana in the past month in 2017. In addition, 6.5% of individuals 12-17 years of age and 22.1% of individuals 18-25 years old used marijuana in the past month, according to the survey. More than 2.5 million individuals between the ages of 12 and 25 who hadn't used marijuana previously started using marijuana last year.
Establishing causal links
Utilizing a more rigorous methodology and genetic approach, new research published in Molecular Psychiatry last month suggests that there is, in fact, a direct, causal relationship between cannabis use and the likelihood than an individual will develop schizophrenia.
Researchers from University of Lausanne in Switzerland, University of Pennsylvania in the United States Oxford University in the United Kingdom and other academic institutions around the world conducted an analysis of already published, observational studies on cannabis use and schizophrenia. The results were then combined with a genetic analysis through complex statistical methods that allowed them to test the link between cannabis use and the development of schizophrenia. This complex study thus mimics a randomized control trial.
From both methods, the researchers found that any cannabis use increases the risk for developing schizophrenia. The genetic approach yielded a 1.37 times increased risk for developing schizophrenia among cannabis users compared to non-users, whereas the meta-analysis found a 1.43 times increased risk.
The findings of this study appear to validate the original hypothesis that use of cannabis increases the risk for developing schizophrenia. Moreover, their complex methodology and genetic test avoids ethical concerns raised by conducting experimental trials on individuals.
The authors are hopeful that their research will "help inform public health debate on cannabis use and preventive strategies to alleviate the burden of disease from schizophrenia." We feel the same.
Elizabeth Sinclair
Director of Research
References:
- Substance Abuse and Mental Health Services Administration. (2018). 2017 National Survey on Drug Use and Health.
- Vaucher, J. et al. (2018). Cannabis use and risk of schizophrenia: A Mendelian randomization study. Molecular Psychiatry.