Tag Archives: @CUBoulder

Twin Study Finds Cannabis Legalization Did Not Cause Substantial Psychological Harm in Adults

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PainRelief.com Interview with:
Stephanie Zellers PhD
Postdoctoral Researcher, Kaprio Group, FIMM
Dr. Zellers began this research as a graduate student at the
University of Colorado Boulder’s Institute for Behavioral Genetics (IBG)

Dr. Zellers PhD

PainRelief.com: What is the background for this study?

Response: Proponents and opponents of cannabis legalization respectively cite various potential benefits and harms that these policies may cause. Many studies have evaluated these outcomes, but drawing causal conclusions is challenging due to the many confounds that may better explain observed effects.

 We investigated the effects of cannabis legalization on a broad range of psychological outcomes, like substance use, psychiatric symptoms, general functioning in daily life, and cognitive ability. We used a longitudinal twin sample with twin pairs living in different types of states (recreationally legal vs. recreationally illegal) to draw causally informative conclusions. Because identical twins share 100% of their genes, as well as environmental factors like the family rearing, SES, and community norms, co-twin control studies can rule out many alternative explanations for an observed relationship.

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Twin Study Find Cannabis Legalization Linked to Increased Marijuana Use in Adults

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PainRelief.com Interview with:
Stephanie Zellers
Psychology
University of Minnesota

PainRelief.com: What is the background for this study?

Response: Many cross-sectional studies have found increases in adult cannabis consumption after the passage of recreational cannabis legalization. These studies, in large population samples across the USA, provide information about possible effects of recreational legalization in representative samples, but cannot draw causally informative conclusions. There are many confounders, like genes, pre-existing differences, and secular trends, that could be alternative explanations for any effects identified.

We utilized a longitudinal twin study to rule out many additional unmeasured confounds shared within families, like genes and aspects of the rearing environment. Importantly, we have data on identical twins before and after recreational legalization, and we have pairs where one twin lives in a recreationally legal state while their co-twin does not. By comparing these twins, we can estimate the causal impact of recreational legalization, after controlling for unmeasured confounds shared by individuals in a family.

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