New data published in the journal Psychological Medicine shows that in states where cannabis has been legalized, residents do not show elevated rates of psychosis. Additionally, residents were less likely to show symptoms of alcohol abuse.

The study’s authors “sought to quantify possible causal effects of recreational cannabis legalization on substance use, substance use disorder, and psychosocial functioning, and whether vulnerable individuals are more susceptible to the effects of cannabis legalization than others.”

Research Methods

To conduct their study, a team of researchers from the University of Minnesota and the University of Colorado looked at the relationship between recreational cannabis legalization and psychosocial functioning. The study followed 240 pairs of twins who lived in different locations. One twin lived in a state with legalized adult-use cannabis and the other twin lived in an area where cannabis use was illegal. The researchers “tested the effect of legalization on outcomes of interest and whether legalization interacts with established vulnerability factors (age, sex, or externalizing psychopathology).”

The Results

Data collected showed that while legalization did appear to result in a slight increase in the frequency with which test subjects used cannabis, it also showed that test subjects in states where cannabis was legal were less likely to engage in problematic alcohol use. 

The study’s authors concluded, “Recreational legalization was associated with increased cannabis use and decreased [alcohol use disorder] symptoms but was not associated with other maladaptations. These effects were maintained within twin pairs discordant for residence. Moreover, vulnerabilities to cannabis use were not exacerbated by the legal cannabis environment. Future research may investigate causal links between cannabis consumption and outcomes.”

Full results of the study appear in the article “Recreational cannabis legalization has had limited effects on a wide range of adult psychiatric and psychosocial outcomes,” in the journal Psychological Medicine.

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