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.
JOURNAL
Addiction
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
People
ARTICLE TITLE
Impacts of Recreational Cannabis Legalization on Cannabis Use: A Longitudinal Discordant Twin Study
ARTICLE PUBLICATION DATE
25-Aug-2022
COI STATEMENT
The authors declare they have no competing interests.
Cannabis legalization boosts use by double-digits
A first-of-its kind study of twins finds those who live in states where marijuana is legal use it 24% more
Peer-Reviewed PublicationResidents of states where cannabis has been legalized use marijuana 24% more frequently than those living in states where it remains illegal, according to new research published today in the journal Addiction.
The study of more than 3,400 adult twins, by researchers at University of Minnesota and University of Colorado, constitutes some of the strongest evidence yet that legalization causes increased use.
It comes at a time when cannabis use is rising nationwide, including during adulthood—a phase of life when individuals have historically tended to cut back.
“Across America, there is a trend toward using more marijuana but we found that the change is bigger in states where it is legal,” said lead author Stephanie Zellers, a recent University of Minnesota graduate who began the research while a PhD student at CU Boulder’s Institute for Behavioral Genetics (IBG).
For the study, Zellers and co-authors at CU Boulder, CU Anschutz Medical Campus and University of Minnesota analyzed data from two large longitudinal twin studies, which have tracked twins since childhood in both states: one housed at IBG and another at the Minnesota Center for Twin Family Research.
Participants were asked how frequently they used cannabis before and after 2014 when Colorado became one of the first states to commence legal sales of recreational marijuana. Recreational cannabis remains illegal in Minnesota. Before 2014, there was little difference in use between states, the study found. After 2014, across all participants, residents of states where recreational use of marijuana was legalized used cannabis 24% more frequently than those in illegal states.
When specifically comparing identical twins in which one now lives in a state where marijuana is legal and the other lives in a state where it is illegal, those living in the state with legal marijuana used cannabis 20% more frequently, the researchers found.
Because twins share their genes and tend to share socioeconomic status, parental influences and community norms, they provide well-matched controls for each other, enabling researchers to minimize alternative explanations for results and get at what causes what.
“This is the first study to confirm that the association between legal cannabis and increased use holds within families in genetically identical individuals,” said co-author John Hewitt, a professor in the Department of Psychology and Neuroscience and faculty fellow at IBG. “This makes it much more likely that legalization does, in itself, result in increased use.”
More than 141 million Americans now live in a state with recreationally legal cannabis and, according to the National Institute on Drug Abuse, use among young adults age 19 to 30 is at an all-time high, with 43% reporting use in the past year and 29% in the last month.
“Typically, what we would expect to see is that people tend to increase use as adolescents and then reduce it as they transition into adult roles, family life and stable jobs,” said Zellers. “Interestingly, we saw escalation, not reduction, in adults.”
The authors note that it is unlikely that legalization would cause those who abstained from marijuana before to pick up the habit.
And preliminary results from their broader ongoing research project suggest increased use may not necessarily be a bad thing.
“In other analyses, we are finding that this increased use is not accompanied by increased problems, may be associated with less alcohol-related problems, and otherwise does not, in general, seem to have adverse consequences,” said Hewitt.
JOURNAL
Addiction
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
People
ARTICLE TITLE
Impacts of recreational cannabis legalization on cannabis use: a longitudinal discordant twin study
ARTICLE PUBLICATION DATE
24-Aug-2022
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