USA study: Cannabis legalization has no relevant effect on psychiatric disorders

February 1, 2023

A twin study from the USA proves the lack of association between legalized cannabis use and the occurrence of psychiatric disorders.   

No link between cannabis legalization and psychiatric disorders 

In a longitudinal study of 4,043 North American twins, researchers from the United States and Finland found that cannabis legalization in the United States had no significant impact on a wide range of psychiatric disorders in adulthood.   

The subjects were first studied in adolescence and again between the ages of 24 and 49. They lived in states where cannabis use is legalized (40 percent) as well as those where it is prohibited.   

Another finding of the study was that the twins who lived in a state with legalized recreational use were more likely to use cannabis but, in turn, less likely to abuse alcohol or be dependent than the sibling pairs in states with cannabis prohibition.   

The study authors conclude that cannabis legalization is not associated with other “adverse outcomes” and encourage further empirical research.   

Cannabis legalization in the USA 

The U.S. has the largest population of cannabis users compared to any other country. Recreational use of cannabis for adults is already legalized in 22 states, with more to be voted on in the future. In October 2022, President Joe Biden announced that there will be sentencing relief for individuals incarcerated for simple cannabis possession – a symbolic act for U.S. states and the international community to support the decriminalization of adult-use cannabis.   

However, restrictions on the cannabis market by the federal government still exist. Regulations and laws prevent cannabis businesses from using banking services, listing on U.S. exchanges, trading across state lines, and importing or exporting products.   

Now, President Joe Biden has ordered decriminalization and a review of the legal status of cannabis. There is hope that cannabis will be reclassified for commercial sale in the near future. 



Zellers, S. M., Ross, J. M., Saunders, G. R. B., Ellingson, J. M., Walvig, T., Anderson, J. E., Corley, R. P., Iacono, W., Hewitt, J. K., Hopfer, C. J., McGue, M. K., & Vrieze, S. (2023). Recreational cannabis legalization has had limited effects on a wide range of adult psychiatric and psychosocial outcomes. Psychological Medicine, 1–10. 


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