Twin Study Finds Cannabis Legalization Did Not Cause Substantial Psychological Harm in Adults What are the main findings?

Response: We found very few differences within twin pairs, with the main exceptions being frequency of cannabis use and endorsement of alcohol use disorder symptoms. Residents of recreationally legal states used cannabis more frequently than their co-twin living in a recreationally illegal state. On the other hand, residents of recreationally legal states endorsed less symptoms of alcohol use disorder compared to their co-twin living in a recreationally illegal state. Specifically, residents of recreationally illegal states were more likely to report engaging in physically hazardous behavior while also consuming alcohol. What should readers take away from your report?

Response: Recreational cannabis legalization does not cause substantial psychological harm in a community sample of adults. We also evaluated several risk factors for cannabis use (age, sex, adolescent externalizing symptoms, adult antisocial personality disorder symptoms) to see if individuals at higher risk for cannabis use were disproportionately affected by recreational legalization. We found no evidence of disproportionate impact on individuals at higher risk for cannabis use. What recommendations do you have for future research as a result of this study?

Response: Future research can evaluate other domains besides psychological outcomes (ex. Physical health, crime) associated with cannabis legalization. Existing risk factors do not appear to be exacerbated in recreationally legal states, but overall, our community-recruited sample was at low levels of risk in terms of prevalence of pre-existing externalizing symptoms. Future work could examine clinical samples composed of participants at higher risk than the present sample. Lastly, future work can investigate different methods of cannabis consumption (edibles, dabs, high-THC potency products, etc.) to evaluate whether certain routes of administration or concentrations are either physically safer or associated with more harmful outcomes. Is there anything else you would like to add? Any disclosures?

Our study is open access and can be read for free in the journal Psychological Medicine at the following link:

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Last Updated on February 1, 2023 by