Legalizing recreational cannabis in the U.S. has increased frequency of use by 20%

A new study published in the scientific journal Addiction has found that the legalization of recreational cannabis in U.S. states appears to have caused a 20% average increase in cannabis use frequency in those states.

The study evaluated the effects of recreational cannabis legalization in a large sample of adult identical twins.  Of particular interest were the 111 identical twin pairs in which one twin lived in a state with a different recreational cannabis policy to the other.  Twins provide extremely well-matched controls for each other and permit more precise estimation of the causal impact of recreational legalization than studies of unrelated individuals.

Looking at all of the study participants (1,425 individuals living in states with legal recreational cannabis use and 1,997 living in states in which recreational cannabis use is illegal), the study found a ~24% increase in mean cannabis use frequency attributable to legalization.  Looking just at the identical twins living in states with different policies, the twin living in a ‘legal’ state used cannabis ~20% more frequently than their cotwin living in an ‘illegal’ state.  These findings suggest that recreational legalization caused an increase in cannabis use.

Cannabis is the most commonly used federally illegal drug in the United States.  It is also an addictive substance associated with negative health and psychosocial outcomes.  Before 2014, cannabis could not be legally bought or sold for recreational purposes anywhere in the U.S. By early 2022, over 141 million Americans lived in a state with recreationally legal cannabis. 

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For editors:

This paper is free to read for one month after publication from the Wiley Online Library: https://onlinelibrary.wiley.com/doi/10.1111/add.16016 or by contacting Jean O’Reilly, Editorial Manager, Addiction, jean@addictionjournal.org.

To speak with lead author Stephanie Zellers please contact her at the University of Minnesota by email (zelle063@umn.edu).

Full citation for article: Zellers SM, Ross JM, Saunders GRB, Ellingson JM, Anderson JE, Corley RP, Iacono W, Hewitt CJ, McGue MK, and Vrieze S (2022) Impacts of Recreational Cannabis Legalization on Cannabis Use: A Longitudinal Discordant Twin Study. Addiction: doi: 10.1111/add.16016

Funding: This work was supported by National Institute on Drug Abuse, National Institute of Mental Health, and National Institute on Alcohol Abuse and Alcoholism of the National Institutes of Health under awards numbers R01DA042755, U01DA046413, R37DA005147, R01DA013240, R01DA036216, R01DA037904, K24DA032555, R01DA035804, P60DA011015, R01DA012845, R01DA038065, R01AA023974, R37AA009367, and R01MH066140.  The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health

Declaration of interests:  The authors declare they have no competing interests.

Addiction is a monthly international scientific journal publishing peer-reviewed research reports on alcohol, substances, tobacco, and gambling as well as editorials and other debate pieces. Owned by the Society for the Study of Addiction, it has been in continuous publication since 1884.