By Columbia Mailman School of Public Health
A study by researchers at Columbia University Mailman School of Public Health and Oregon State University based on national data found that in states where recreational marijuana has been legalized, young adults who were not in college more often became frequent users of the drug than those in other states. The findings are published in the American Journal of Preventive Medicine(link is external and opens in a new window).
After state legalization, young adults also were more likely to meet the criteria for cannabis use disorder, meaning that they continued to use the drug despite problems it caused in their lives. These patterns were not found in young adults who were in college.
The study used data from the National Survey on Drug Use and Health from 2008-2019, which surveyed college-eligible young adults ages 18-23 about their drug and alcohol use. The dataset is representative of the demographics of young adults nationally and at the state level, and the study covers a longer stretch of time post-legalization than previous research, according to the researchers.
“It might surprise people that research has been mixed on whether young adults’ cannabis use has increased since legalization,” said David Kerr, PhD, professor in OSU’s School of Psychological Science and first author. “Our results show that prior to legalization 23 percent of non-college young adults used cannabis in the past month, compared to 28 percent after legalization.”
While the percentage of non-college young adults who reported past-month cannabis use increased by 5 percentage points, it only increased by 1 percentage point among college students in the same age bracket, from 20 percent to 21 percent.
Frequent cannabis use—using the drug at least 20 times in the past month—also increased more among non-college young adults, from 12 percent to 14 percent. The prevalence for college students was 7 percent and did not change after legalization. Kerr noted that the research did not account for the fact that the potency of cannabis is higher in legal states and has increased dramatically over time.
Cannabis use disorder among non-college participants also grew from 12 percent to 15 percent while staying the same, at 10 percent among college students.
“Our research doesn’t address why these changes are occurring, but if you’ve been to a state that has legalized recreational cannabis use you’ll notice the drug is widely available and prominently advertised. Americans’ beliefs about the benefits and harms of cannabis use are also changing rapidly,” Kerr said, citing a report from the Monitoring the Future study showing that in 2020 only 21 percent of young adults believed regular cannabis use puts people at risk of harm, compared to 58 percent of young adults 20 years ago.
Increased acceptance of cannabis use at the societal level could affect the rate at which users experience cannabis use disorder, the authors note, because many of the negative consequences associated with the disorder are social in nature.
“Cannabis use disorder involves inability to fulfill major obligations at work, school or home, and then continued use,” Kerr said. “It is possible that there may be fewer social consequences now that the environment is more accommodating,” he said. “If so, then our findings may actually have underestimated these increases,” he added.
The study also found that in states where legalization occurred, recent cannabis use increased more among young adults ages 21-23 (from 21 percent to 26 percent) than among 18-20-year-olds (from 22 percent to 23 percent).
“That’s consistent with our prior work, that it increased more among the people who could legally buy it and use it,” Kerr said. “It suggests the law provisions requiring people to be at least 21 are at least somewhat effective.”
“Researchers should continue to monitor changes in prevalence of cannabis use, frequent cannabis use and cannabis use disorder among young adults while the cannabis landscape in the U.S. continues to evolve,” said senior author Silvia Martins, MD, PhD, professor of Epidemiology at Columbia Mailman School of Public Health. “It is also important to better understand why increases to date were more pronounced in young adults not in college.”
Co-authors are Natalie Levy, Columbia University Mailman School of Public Health; Harold Bae, Oregon State University; and Anne Boustead, Arizona State University.
The research was funded by a grant from the National Institute on Drug Abuse.
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