Twin Study Find Cannabis Legalization Linked to Increased Marijuana Use in Adults Interview with:
Stephanie Zellers
University of Minnesota 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.