Twin Study Assesses Alcohol Use Disorder in States with and without Legal Cannabis

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The study, which began before states started legalizing cannabis, published its results on the impact of a legal cannabis environment on cannabis use and alcohol use disorder.

A peer-reviewed, longitudinal study recently published in the journal Psychological Medicine suggested that people who live in states where cannabis was legal experienced lower rates of alcohol use disorder (AUD) compared to those who lived in states where cannabis was illegal (1). The study, funded by grants from the National Institutes of Health, involved 240 pairs of twins (one twin living in a state with legalized cannabis, and the other twin in a state where cannabis was illegal) and sought to quantify the impact of recreational cannabis on substance use, day-to-day functioning, and whether vulnerable people are more susceptible to potential negative effects than others (1).

The “Results” section of the paper stated (2): “In the co-twin control design accounting for earlier cannabis frequency and alcohol use disorder symptoms respectively, the twin living in a recreational state used cannabis on average more often, and had fewer AUD symptoms than their co-twin living in a non-recreational state. Cannabis legalization was associated with no other adverse outcome in the co-twin design, including cannabis use disorder. No risk factor significantly interacted with legalization status to predict any outcome.”


“Recreational legalization was associated with increased cannabis use and decreased AUD symptoms, but was not associated with other maladaptations” (2), the authors of the study concluded. “Moreover, vulnerabilities to cannabis use were not exacerbated by the legal cannabis environment.”

The authors did acknowledge that not all outcomes typically associated with cannabis use were evaluated and that a broadly characterized sample population was used (1). In its conclusion, the study suggested that further research could investigate causal links between cannabis consumption and outcomes (2). “Prevention and intervention efforts may be best implemented by continuing to target established risk factors rather than focusing on availability,” they also concluded (1).