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Five years after the legalization of cannabis in Canada, cannabis use frequency has risen slightly, and cannabis misuse has decreased, new data suggested.

A prospective cohort study of 1428 adults indicated that the mean proportion of days using cannabis increased by 0.35% annually and by 1.75% over 5 years. Cannabis misuse decreased annually (β = −0.08) and over 5 years (β = −0.4). Prelegalization use frequency influenced the use and misuse of cannabis after legalization.

“It is important to note that both effect sizes were quite small, so we are looking at modest changes,” lead author André J. McDonald, PhD, a postdoctoral fellow at McMaster University in Hamilton, Ontario, told Medscape Medical News. “Still, our finding that cannabis use frequency increased is concerning from a public health perspective.”

The study was published on April 23 in JAMA Network Open.

Use Over Time

“The hypothesis, based on previous studies, was that cannabis use and misuse had increased in the adult population,” said McDonald. “It is important to place this [study] within the broader literature, which predominantly suggests that cannabis use and misuse have increased. This, however, is a different study design, and so it gives a more nuanced description of what those trends are over time.” The current study’s longitudinal design enables distinctions in use and misuse within subsets of the study population, he added.

The investigators asked participants about the proportion of days that they used cannabis in the past 6 months to determine cannabis use frequency. They employed the Cannabis Use Disorder Identification Test–Revised (CUDIT-R) scale to determine cannabis misuse. Prelegalization cannabis use frequency, age, and sex were examined as moderators of these two outcomes. Secondary endpoints included changes in cannabis product preferences over time.

“Amongst those who were using frequently before legalization, we did not see an increase in their use or misuse,” said McDonald. “A positive [outcome] is that legalization did not exacerbate some of those issues. If anything, we found that for those who were using frequently before legalization, generally, their cannabis use and misuse decreased over time.”

Investigators observed annual changes of −5.26% in the proportion of days using and −0.63 in the CUDIT-R score among prelegalization daily users.

The researchers observed that the decline in cannabis misuse primarily occurred among younger people. The CUDIT-R score changed by −0.12 in participants younger than 30 years.

“There is a typical pattern where problematic substance use peaks in early adulthood and then gradually discontinues,” said McDonald. “That is consistent with what we saw in our cohort.”

Cannabis Preferences Shifted

Investigators observed that participants’ cannabis product preferences shifted. There were statistically significant decreases in the use of dried flower, solid concentrate, liquid concentrates, cannabis oil, tinctures, topical ointments, and hashish. They also found statistically significant increases in the use of edibles, liquids, and cannabis oil cartridges or disposable vape pens, noted McDonald.

The most pronounced decline was in dried flower use, with a 3.56% annual decrease in prevalence among active cannabis users (from 81.3% before legalization to 64.6% at 5 years postlegalization). The most pronounced increase was in the use of cannabis oil cartridges or disposable vape pens, with a 3.39% annual increase in prevalence among active cannabis users (from 18.4% before legalization to 33.0% at 5 years postlegalization).

“It could be viewed positively, in that people are transitioning away from the combustible products,” said McDonald. He noted, however, that some vape products have high tetrahydrocannabinol content.

Benefit of Categorization

Commenting on the study for Medscape Medical News, Sameer Imtiaz, PhD, staff scientist at the Center for Addiction and Mental Health’s Institute for Mental Health Policy Research and assistant professor of psychiatry at the University of Toronto, Toronto, remarked that categorizing users by cannabis use and comparing patterns of use before and after legalization is noteworthy. Imtiaz did not participate in the research.

“The findings are novel and interesting,” said Imtiaz. “Specifically, the moderating role of cannabis use frequency before cannabis legalization is noteworthy, as those who used cannabis more frequently before cannabis legalization demonstrated larger decreases in cannabis use frequency and cannabis misuse after cannabis legalization. Such insights are often not available from studies with repeated cross-sectional designs.”

Imtiaz commended the investigators for the study’s robust methodology, including the prospective cohort design, measurement of use and misuse before legalization, long-term follow-up after legalization, biannual repeated measurements, large sample size, high retention rate, inclusion of validated measures, and appropriate statistical methods.

Given that the study sample mostly comprised women (60%), highly educated (92% with some postsecondary education), and unmarried (68%) participants, the generalizability of the findings is limited, noted Imtiaz.

The study was supported by the Canadian Institutes of Health Research, a Canada Research Chair in Translational Addiction Research grant, and the Peter Boris Chair in Addictions Research. McDonald and Imtiaz reported no relevant financial relationships.