How Legalization Changed Youth Cannabis Risk

A new study¹ from the University of Waterloo’s COMPASS program challenges early fears that legal cannabis would spark widespread use among teens in Canada.  Interestingly, after analyzing data from 85 secondary schools, researchers found that youth cannabis use actually declined slightly—from 15.0% in 2017–18 to 12.3% in 2021–22—while the number of students who had never used increased.

In addition to declining usage overall, those who do partake have also changed.  Before legalization, a higher chance of use was tied to skipping homework and heavy texting.  Four years later, mental-health signs such as anxiety, depression, and not eating breakfast became stronger predictors of cannabis use.

Context Matters: The Mature vs. Developing Brain

It is important to remember that cannabis is not inherently harmful — in fact, research shows that in mature adults, it can offer therapeutic benefits for pain, sleep, anxiety, and overall quality of life when used responsibly.  The concern in youth research is developmental timing.

The adolescent brain is still refining emotional regulation, reward sensitivity, and executive function — areas more easily influenced by high-THC exposure.  Prevention, therefore, isn’t about demonizing cannabis; it’s about giving young people the best chance to reach adulthood with their full cognitive and emotional potential intact.

What Changed—and Why It Matters

How Mental-Health Factors Replaced Behavioral Risk in Youth Cannabis Use

Before legalization, the highest-risk group was large and easily described: students who de-prioritized grades and spent ≥45 minutes/day texting had a 26.9% probability of current use.  Post-legalization, the top-risk group (27% probability) still de-prioritized grades but also skipped daily breakfast and screened high for anxiety.  Depression, flourishing, and emotion regulation also entered the model as influential correlates.

This migration of risk factors toward internalizing mental health suggests a broader social transition: as cannabis became less stigmatized for adults, youth use may have shifted away from purely deviant peer behavior toward self-medication for stress, low mood, and sleep problems.  That aligns with recent data showing young people increasingly report using substances to manage anxiety and sleep—trends that have intensified since the pandemic.

Why Small Declines Can Mask Big Mental-Health Risks

A few percentage-point decline in current use can mask rising vulnerability within specific subgroups.  Decision trees are valuable because they surface high-risk “micro-populations”—for example, students with low academic valuation plus anxiety—who may not be visible in school-wide averages.  Targeting these branches can prevent disproportionate harm.

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Forward Look: How to Support Youth in the Next Four Years

1) Integrate Mental Health and Cannabis Education

If anxiety, depression, and poor emotion regulation now predict cannabis use, then mental-health support is not separate from substance education — it is substance education.  Schools can normalize mental-health conversations, provide quick access to counseling, and teach practical coping skills through CBT or DBT-based programs.  When students understand how stress and sleep affect their choices, they can decide more consciously whether cannabis fits into their coping toolbox — and learn safer alternatives when it doesn’t.

2) Strengthen Connection and Engagement

Academic engagement remains protective, but the path there is relational, not disciplinary.  Teachers and advisors who check in early with students showing signs of withdrawal, low motivation, or absenteeism can make a real difference.  Small nudges — flexible deadlines, recognition for effort, or breakfast programs that build daily routine — support both wellness and school connection.  The goal isn’t compliance; it’s belonging and stability, which naturally reduce risky coping behaviors.

3) Shift from “Don’t” to “Understand How Risk Builds”

Young people are savvy.  They know fear-based messaging doesn’t match their lived reality.  Instead, education should explain mechanisms: how THC affects developing brains, how tolerance and high potency can amplify anxiety, and why balance (lower-THC, terpene-rich products, moderation) matters.  Framing cannabis discussions around physiology and emotional awareness fosters critical thinking rather than stigma — and encourages delay or moderation without alienation.

4) Use Data to Personalize, Not Punish

Schools already collect valuable non-identifying indicators — attendance, homework engagement, counseling referrals.  These can be ethically leveraged to flag students who might need extra support.  insights should guide outreach, not discipline.  A student showing anxiety and academic decline may need a listening ear, not a lecture.

5) Prepare for Changing Products and Motivations

Legal markets keep evolving — from rapid-onset edibles to high-THC vapes and minor-cannabinoid blends.  Prevention efforts should evolve too, offering up-to-date information about potency, effects, and safer-use strategies.  For older teens approaching legal age, it’s more realistic — and responsible — to discuss moderation, product choice, and self-awareness than to pretend use won’t occur.  Informed youth make safer decisions.

What This Means for Policymakers and Public Health

Target resources where risk clusters

Grant programs should prioritize school-mental-health capacity (counselors trained in adolescent anxiety/depression + substance use), breakfast and nutrition access, and engagement micro-interventions.  Funding should reward districts that implement, non-punitive supports for students flagged by multi-factor risk profiles.

Harmonize prevention with legal-market realities

Clearer point-of-sale messaging (e.g., “not for sleep problems,” “can worsen anxiety in teens”) and plain-language potency labeling can complement school efforts.  Partnerships with community clinics can offer brief interventions for at-risk youth and family education tailored to the new risk landscape.

Where Research Should Go Next

The decision-tree signals are hypotheses for action, and they open a practical research agenda:

• Test whether bundled supports (anxiety treatment + homework coaching + breakfast access) reduce initiation and progression more than any single program.
• Track sleep and mood trajectories in at-risk students to see whether early support prevents the transition to habitual coping use.
• Map how product types and potencies interact with internalizing symptoms across adolescence, so prevention messaging can be specific, not generic.

Bottom Line

Legalization did not unleash widespread increases in underage cannabis use in these schools; if anything, current use declined modestly.  But risk did not vanish—it shifted.

Today, the youth most likely to use are increasingly those struggling internally while disconnecting academically.  The most effective prevention in the legalization era is therefore mental-health-centered, academically supportive, and analytically targeted.  If schools, clinicians, and public-health leaders adapt to that reality now, the next four years can deliver larger reductions in harmful patterns—without stigmatizing students who need help the most.

Legalization recognizes that cannabis can play a positive role for many adults — easing pain, improving sleep, and supporting wellness.  The goal for youth prevention isn’t to deny those realities but to ensure that developing minds reach adulthood before exploring those same benefits safely and intentionally.

References:

^{1. Leatherdale, S. T., Battista, K., Patte, K. A., MacKillop, J., & Bélanger, R. (2025). Using decision trees to examine risk profiles for cannabis use among large samples of underage youth before and after cannabis legalization in Canada. Addictive Behaviors Reports, 100632. https://doi.org/10.1016/j.abrep.2025.100632}