Study: Marijuana Legalization Associated With a Reduction in Alcohol Use Disorder, No Increase in Psychosis

The state-level legalization of recreational marijuana is associated with a reduction in alcohol use disorder, according to a study published by the journal Psychological Medicine.

The causal impacts of recreational cannabis legalization are not well understood due to the number of potential confounds”, states the study. With this in mind, researchers “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.”

Researchers from the University of Colorado and University of Minnesota used a longitudinal, co-twin control design in 4,043 twins, first assessed in adolescence and now age 24-49, currently residing in states with different cannabis policies (40% resided in a recreationally legal state). Researchers tested the effect of legalization on outcomes of interest and whether legalization interacts with established vulnerability factors (age, sex, or externalizing psychopathology).

“In the co-twin control design accounting for earlier cannabis frequency and alcohol use disorder (AUD) symptoms respectively, the twin living in a recreational state used cannabis on average more often (βw = 0.11, p = 1.3 × 10-3), and had fewer AUD symptoms (βw = -0.11, p = 6.7 × 10-3) than their co-twin living in an non-recreational state”, the study found. “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.”

The study concludes that recreational legalization “was associated with increased cannabis use and decreased AUD 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.”

More information on this study can be found by clicking here.

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