Among 961 high-risk emerging adults tracked over two years, negative consequences from cannabis use predicted subsequent depressive symptoms more strongly than the reverse, particularly among women.
Clinical psychologists, young adult mental health providers, harm reduction advocates, substance use researchers
What the researchers found
Using seven assessments over two years, significant bidirectional within-person relationships were found between cannabis consequences and internalizing symptoms, but the primary direction was from cannabis consequences to increased depressive symptoms, not from depression to increased cannabis use. Importantly, cannabis use frequency alone did not predict later symptoms; only negative consequences did. The bidirectional relationships were more pronounced among females and those with clinically elevated internalizing symptoms at baseline.
Why it matters
This clarifies a longstanding debate: it is the problems from cannabis use (not the use itself) that predict worsening mental health. This distinction has practical implications, as interventions that reduce cannabis-related harm could prevent downstream depression even without full abstinence.
The numbers in context
961 emerging adults; 54% female; 7 assessments over 2 years; cannabis consequences predicted depressive symptoms (within-person); frequency alone did not predict symptoms; effects stronger in females and those with clinical-level baseline symptoms
How the study worked
Longitudinal study of 961 high-risk emerging adults (54% female) from two cohorts (Ontario, Canada and Tennessee, USA), assessed at 4-month intervals over 2 years (2018-2020). Latent curve models with structured residuals examined within-person and between-person bidirectional relationships.
What this study cannot tell us
High-risk sample may not generalize to general population. Self-report measures. Study period overlapped with early COVID-19 pandemic. Four-month intervals may miss shorter-term dynamics. Consequences and symptoms may share reporting bias.
How to read the evidence
Moderate: strong longitudinal design with multiple assessments and advanced modeling, but self-report measures and high-risk sample.
When this study was published
2025 publication using 2018-2020 data
The bigger picture
The finding that consequences, not frequency, drive the mental health link suggests that harm reduction approaches, which aim to reduce negative outcomes without requiring abstinence, may be effective for preventing depression in young cannabis users.
Questions still open
- Would harm reduction interventions that reduce cannabis consequences also prevent depressive episodes?
- Why are females more vulnerable to this bidirectional relationship?
Read the original research
Examining bidirectional associations between cannabis use and internalizing symptoms among high-risk emerging adults: A prospective cohort study.
Psychological medicine, 55, e291
Citation
Halladay, Jillian; Belisario, Kyla; McDonald, André; Acuff, Samuel; Doggett, Amanda; Garber, Molly; Maxwell, Andrea; Murphy, James; MacKillop, James. (2025). Examining bidirectional associations between cannabis use and internalizing symptoms among high-risk emerging adults: A prospective cohort study.. Psychological medicine, 55, e291. https://doi.org/10.1017/S0033291725101700
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