Twin study shows legalizing recreational cannabis does not increase substance abuse

Bar graph depicting the effects sizes of recreational legalization as generated from the individual level and MZ-DZ combined co-twin analyses. One asterisk represents significance at p < 0.05 and two asterisks represent significance at the multiple testing corrected threshold p < 0.0023. Positive betas indicate increased mean levels in recreational states, negative betas indicate decreased mean levels in recreational states. Notable effects are higher cannabis use frequency within twin pairs for the twin living in a recreationally legal state, as well as decreased AUD symptoms within twin pairs for the individual living in a recreationally legal state. Error bars represent standard error of linear-mixed effects model estimates as generated by the function lmer in the package lme4. Credit: Psychological Medicine (2023). DOI: 10.1017/S0033291722003762

Legalizing recreational cannabis at the state level does not increase substance use disorders or use of other illicit drugs among adults and, in fact, may reduce alcohol-related problems, according to new CU Boulder research.

The study of more than 4,000 twins from Colorado and Minnesota also found no link between cannabis legalization and increases in cognitive, psychological, social, relationship or financial problems.

“We really didn’t find any support for a lot of the harms people worry about with legalization,” said lead author Stephanie Zellers, who began the research as a graduate student at CU Boulder’s Institute for Behavioral Genetics…

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