Legalizing Marijuana For Adults Does Not Drive Increases In Youth Use, New Federally Funded Study Finds

New federally funded research into the impacts of marijuana legalization on youth use found no association between legal adult-use cannabis sales and the prevalence of consumption among middle-school students.

To test whether legal sales led to an uptick in youth use, authors compared middle-school use rates in Nevada and New Mexico, looking at 2017 and 2019 data from two state-run surveys. At the time, adult-use marijuana sales were legal in Nevada, while New Mexico allowed only medical marijuana.

In both states, researchers found increases in the proportions of students that had ever consumed cannabis as well as those who had consumed within the past 30 days.

In Nevada, the share of middle-school students who said they’d ever consumed cannabis rose during the study period, from 9.7 percent in 2017 to 13.3 percent in 2019. Past 30 day (P30D) use also rose, from 6.3 percent to 8.9 percent.

New Mexico, where recreational marijuana remained illegal, saw lifetime use rise from 14.1 percent to 17.4 percent over the same period. Past 30 day use rose from 8.9 percent to 10.5 percent.

“There was no difference in lifetime marijuana use by adult-use sales status.”

Researchers called the increases concerning, but they said they said legalization likely wasn’t the culprit.

“We did not find compelling evidence that the implementation of adult-use marijuana sales was associated with an immediate increase in lifetime or P30D marijuana use among middle school youth in Nevada, which aligns with previous research,” the study says. “However, the increase in marijuana use among middle school students in both Nevada and New Mexico from 2017 to 2019 is concerning given the negative health consequences associated with initiation of marijuana use at an early age.”

Likewise, the “effect of adult-use marijuana sales on lifetime and P30D marijuana use was not statistically significant,” it adds.

The paper, by researchers at the University of Nevada, University of New Mexico and the New Mexico Department of Health, is in the June 2024 issue of the journal Addictive Behaviors and was posted online late last month. It was funded with a grant from the National Institute on Drug Abuse (NIDA), a federal agency.

Across the two states, respondents who were female, nonwhite and attended a low-income Title I school were associated with higher odds of both lifetime and past 30 day cannabis use.

“Our results are consistent with literature that identifies marijuana use as a mechanism for coping with poverty and discrimination,” authors wrote, “and literature that shows adolescent females are now reporting more marijuana use than their male counterparts.”

The new study’s findings suggest that policymakers aiming to reduce youth cannabis consumption rates should focus on prevention among groups most at risk—not simply whether or not the substance is legal for adults.

“Adult-use sales were not associated with an increase in lifetime or P30D marijuana use.”

“State level prevention efforts should focus on sub-populations with an increase in lifetime or P30D marijuana use regardless of adult-use legalization status,” the study says. “Our findings suggest a need for primary intervention, particularly for females, students of color, and those attending Title I schools. As more states legalize adult-use marijuana sales, it is imperative that state-level surveillance systems monitor substance use trends during early adolescence.”

Authors acknowledged some limits to the new research, including the fact that both Nevada and New Mexico neighbor states with their own cannabis policies. Specifically, the wrote that they “could not control for the possible influence of neighboring states that have legalized marijuana such as Colorado and California.”

They also did not examine frequency of use or changes in cannabis use disorder.

“While there is a need for more robust research evaluating the impact of adult-use marijuana sales on marijuana use among middle school students,” the paper says, “our research highlights an immediate need for prevention efforts for youth at greatest risk, regardless of state legalization.”

The study is consistent with other findings around youth use and legalization. As an official at NIDA put it late last year, state-level legalization has “not really impacted” rates of marijuana use among young people.

“Whatever is happening with adult-use [legalization] across the country has not really impacted the younger people, according to the data here,” Marsha Lopez, chief of NIDA’s epidemiological research branch, said at an event in December.

Data nevertheless suggests the use of marijuana as well as certain psychedelics among adults have reached “historic highs” in recent years.

But youth, according to a separate study last year, are not more likely to use marijuana after legalization. “No statistically significant differences were found in the prevalence of past-30 day cannabis use before and after legalization among adolescents,” that report said. The proportion of students who reported perceiving that a parent uses cannabis, however, rose from 18 percent to 24 percent after legalization.

Another analysis last year from the Centers for Disease Control and Prevention (CDC) found that rates of current and lifetime cannabis use among high school students have continued to drop amid the legalization movement.

Despite widespread concerns that legalization would lead to a massive increase in youth cannabis use, most available evidence suggests the impacts have been minimal and in some cases even reduced use by minors. A study of youth use in Canada published in September in the Journal of the American Medical Association (JAMA) Network Open, for example, found that young adults who used marijuana frequently before legalization “showed significant reductions in use and consequences” following the policy change.

While some infrequent marijuana users did increase their consumption after legalization, that study found, “such an increase did not lead to problematic outcomes during the study period.”

In the U.S., federally funded research published in August found that teen use of marijuana remained stable amid the legalization movement even as adult use of cannabis and psychedelics reached “historic highs.”

A recent Gallup poll, meanwhile, found that fully half of all American adults have tried marijuana at some point in their lives, with rates of active cannabis consumption surpassing that of tobacco. Broken down by age, 29 percent of those 18–34 say they currently smoke marijuana, though that’s not necessarily representative of overall cannabis use, because the survey only asked about smoking and not other modes of consumption such as edibles, vaping or tinctures.

A separate NIDA-funded study published in the American Journal of Preventive Medicine last year also found that state-level cannabis legalization is not associated with increased youth use. That study observed that “youth who spent more of their adolescence under legalization were no more or less likely to have used cannabis at age 15 years than adolescents who spent little or no time under legalization.”

Yet another federally funded study from Michigan State University that was published in the journal PLOS One last year found that “cannabis retail sales might be followed by the increased occurrence of cannabis onsets for older adults” in legal states, “but not for underage persons who cannot buy cannabis products in a retail outlet.”

Prohibiting cannabis may, however, push more teens toward the use of unregulated delta-8 THC, according to a study published this month by the American Medical Association. In states where marijuana remains prohibited, 14 percent of high-school seniors said they had used a delta-8 product in the past year, the federally funded research found. Where marijuana was legal, that figure was 7 percent.

A separate report published earlier this year by a CBD manufacturer, meanwhile, found that internet search interest in delta-8 THC was significantly higher in states where marijuana itself remains criminalized. The company said the findings indicated “a significant pivot toward alternative cannabinoids due to cannabis bans.”

Yet another report, published a year ago by the Department of Defense, found that delta-8 THC was the second most common substance to appear on positive drug tests for active duty military service members. Delta-8 THC showed up in 42.7 percent of positive drug tests, the department said, second only to marijuana.

Psychedelic Use Linked To ‘Lower Rates Of Psychotic Symptoms’ In Adolescents, Study Published By American Medical Association Finds