Longitudinal changes in cannabis use and misuse in the 5 years following recreational cannabis legalization in Canada: A prospective cohort study of community adults
Bibliographic record
Abstract
Abstract Importance A growing number of jurisdictions have legalized recreational cannabis for adults, but most evaluations have used repeated cross-sectional designs, preventing examination of within-person and subgroup trajectories across legalization. Objective To examine changes in cannabis use and misuse in the five years following legalization in Canada – the first G7 country to legalize adult recreational cannabis use – both overall and by pre-legalization cannabis use frequency using a longitudinal design. Design Prospective cohort study with 11 biannual assessments from September 2018 to October 2023. Mean retention was 90% across all waves. Setting Ontario, Canada. Participants Sample of 1,428 (60.2% female, M age =34.5) community adults aged 18 to 65 years. Exposure Five years of recreational cannabis legalization (the baseline wave was immediately prior to legalization). Main outcome and measures Primary outcomes were cannabis use frequency and cannabis misuse (CUDIT-R score). Pre-legalization cannabis use frequency, age, and sex were examined as moderators. Secondary outcomes included changes in cannabis product preferences over time. Results Linear mixed effects modelling found a significant increase in cannabis use frequency, such that the mean proportion of days using cannabis increased by 0.35% ( p <.001) per year in the overall sample (1.75% over 5 years). In contrast, CUDIT-R scores (on scale of 0 to 32) decreased significantly overall (b=-0.08 [-0.4 over 5 years], p <.001), most notably following the onset of the COVID-19 pandemic. Interaction analyses indicated that pre-legalization cannabis use frequency significantly moderated changes for both outcomes ( p <.001). Specifically, cannabis use and misuse decreased among pre-legalization frequent consumers and modestly increased among occasional/non-users. Cannabis product preferences shifted away from dried flower, hashish, concentrates, oil, tinctures, and topicals to edibles, liquids, and vape pens. Conclusions and Relevance In the five years following legalization, cannabis use frequency increased modestly, while cannabis misuse decreased modestly in a longitudinal observational cohort of Canadian adults. These changes were substantially moderated by pre-legalization cannabis use, with more frequent consumers of cannabis pre-legalization exhibiting the largest decreases in both outcomes. Although longer-term surveillance is required, these results suggest Canadian recreational cannabis legalization was associated with modest negative consequences and some evidence of positive outcomes among nonclinical community adults. Key points Question Did cannabis use or misuse change among adults in the five years following recreational cannabis legalization in Canada (overall and by pre-legalization cannabis use frequency)? Findings Overall, cannabis use frequency increased significantly while misuse decreased significantly, with small effect sizes for both. Pre-legalization cannabis use significantly moderated these changes. Product preferences shifted from dried flower, hashish, and concentrates to edibles, liquids, and vape pens. Meaning From a public health standpoint, these findings suggest both a modest negative consequence (small increase in cannabis use frequency) and positive outcomes (small decrease in cannabis misuse, and transition from combustible to non-combustible products).
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.003 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".