Young adults who used marijuana frequently before legalization “showed significant reductions in use and consequences” following the policy change, according to a new study of Canadian data published by the American Medical Association that challenges the widespread worry that ending prohibition will lead to a dangerous rise in youth cannabis use.
Consumption did tick up slightly among young adults who claimed not to have used marijuana prior to legalization, but that slight rise didn’t lead to a corresponding increase in cannabis-related consequences, says the study, published on Wednesday in the Journal of the American Medical Association (JAMA) Network Open.
“These findings suggest that across Canadian cannabis legalization, high-risk young adults showed different patterns of change,” wrote the six-person research team. “Those using cannabis frequently prelegalization exhibited reductions consistent with aging out, and those not using cannabis prelegalization exhibited modest increases in use over time.”
Authors noted that despite common fears that legalization might lead to higher rates of teen marijuana use, “there is a dearth of research focusing on this population.”
“In all jurisdictions where cannabis legalization takes place, a key concern has been that cannabis use and related harms would increase among youths and young adults due to easier access, growing social acceptability, declining perception of harm, lower prices, a wider array of products and modes of use, and increasing product potency,” the study acknowledges, noting that young adults typically have the highest rates of cannabis use as well as the highest prevalence of cannabis use disorder.
Nevertheless, it continues, “there have been few longitudinal studies examining the impact of legalization, which represents a substantial research gap.”
Overall, both mean cannabis use frequency and cannabis use consequences overall decreased over time as legalization took effect. But authors acknowledge that it’s not entirely clear whether the policy shift actually caused the results or whether such patterns would have held regardless of legalization.
“Rather than detecting increases,” the report says, “the results revealed decreases overall, which is broadly consistent with substance use trajectories that might be expected among this age group in absence of any policy change. Correspondingly, the changes observed in this study did not appear to be markedly changed by cannabis legalization.”
To arrive at the conclusions, authors surveyed young adults, ages 19.5 to 23, who reported two or more “heavy episodic drinking episodes.” The criteria were “intended to recruit a sample with epidemiologically common patterns of substance use associated with elevated risk for adverse consequences.” Participants were then surveyed on consumption and “related consequences” both before and after marijuana legalization in Canada took effect.
All told, 619 people were included in the survey. Of those, 55.9 percent were female (gender and sex “overlapped 99.7 percent” authors wrote), and 53.3 percent had a bachelor’s degree or higher. People with current or past experiences of psychosis were excluded.
Prior to legalization, about a third (31.6 percent) of participants said they used marijuana regularly or frequently. Another third (33.3 percent) said they used only occasionally, while another third (35 percent) reported either never or not currently using cannabis.
Participants were surveyed about their marijuana use as well as on so-called “cannabis-related consequences” as measured through the B-MACQ—a brief, 21-question version of the Marijuana Consequences Questionnaire (MACQ) that includes statements such as “I haven’t been as sharp mentally because of my marijuana use,” “I have been overweight because of my marijuana use,” and “I have neglected obligations to family, work, or school because of my marijuana use.”
Among those who used cannabis only occasionally, use typically either increased or decreased following legalization: 32 percent transitioned to no use at all and 23 percent transitioned to regular use. Only 40 percent of occasional users remained occasional users after legalization.
Among other participants, trends differed based on frequency of use prior to legalization.
“Individuals using cannabis most frequently prelegalization exhibited, on average, a significant reduction in use postlegalization. Correspondingly, this group also exhibited a significant reduction in cannabis-related consequences,” the study found. “In contrast, participants who were not recent cannabis users prelegalization increased their frequency of use over time, on average.”
Among the latter group, authors noted, “although frequency increased in this subgroup, such an increase did not lead to problematic outcomes during the study period.”
Participants who had never used marijuana prior to legalization, the study found, “exhibited no significant increases in use or consequences postlegalization.”
As for marijuana-related consequences, authors acknowledged that a “B-MACQ score of 0 (no cannabis-related consequences) was most prevalent prelegalization and postlegalization; however, this category grew between these time points.” Prior to legalization, 51 percent of respondents reported no such consequences. After legalization, that proportion climbed slightly to 57 percent. “This was our most stable category over time,” the team wrote.
Meanwhile, those participants who reported one to four cannabis-related consequences prior to legalization generally saw consequences decrease. Forty-seven percent reported no consequences after legalization, while 16 percent experienced five or more consequences.
“Those in the frequent cannabis use category generally maintained high levels of cannabis use and consequences over time,” the study says; “69 of those using frequently prelegalization (77%) remained in that category postlegalization, and 76 of those with a B-MACQ score of 5 or more prelegalization (56%) were still experiencing 5 or more cannabis-related consequences postlegalization.”
Authors of the Canadian study said it “aligns with research from U.S. jurisdictions which have largely found that legalization has not drastically altered consumption patterns among youth and young adults”—in part because marijuana use was fairly mainstream even during prohibition.
“The lack of considerable considerable change over such a large-scale policy shift could be because cannabis use in Canada was already quite normalized prelegalization,” they wrote. “Prelegalization perceptions among Canadians who used cannabis were that it was already fairly easy to access, and risk perceptions were generally low. As such, any changes in access or social acceptability brought on by cannabis legalization may have been fairly inconsequential on individual use patterns in this age group.”
Researchers said in conclusion that “further longitudinal surveillance is critical to evaluate the consequences of cannabis legalization empirically and promote evidence-informed public policy.”
In the U.S., federally funded research published last month found that teen use of marijuana remained stable amid the legalization movement even as adult use of cannabis and psychedelics reached “historic highs.”
A Gallup poll released last month, 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 National Institute on Drug Abuse-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.”
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