An analysis of 410,138 NSDUH respondents found cannabis exposure was significantly associated with all four measures of mental illness across US regions and time, with serious mental illness doubling as cannabis use increased.
Mental health epidemiologists, cannabis policy makers, and public health officials in legalized states.
SMI doubled (3.62% to 7.06%) as cannabis use increased; legalization AFE 12.91%
What the researchers found
Across 410,138 NSDUH respondents (76.7% response rate), cannabis exposure was significantly associated with any mental illness, major depression, serious mental illness (SMI), and suicidal ideation in geospatial models adjusted for demographics and other substance use. SMI rates doubled (3.62% to 7.06%) as cannabis use increased across regions. Cannabis decriminalization was associated with a 3.28% attributable fraction of SMI, and legalization with 12.91% attributable fraction.
Why it matters
This is one of the first studies to apply formal causal inference methods to the cannabis-mental health relationship at a population level, finding dose-response and temporal-sequential relationships consistent with causation.
The numbers in context
410,138 respondents; 76.7% response rate; SMI doubled from 3.62% to 7.06% with cannabis increase; decriminalization AFE 3.28%; legalization AFE 12.91%; significant for all 4 MH outcomes.
How the study worked
Ecological cohort study using NSDUH geographically-linked substate data (2010-2012 and 2014-2016) with two-stage geotemporospatial robust generalized linear regression and formal causal inference analysis.
What this study cannot tell us
Ecological design (associations at area level may not hold for individuals); cross-sectional components within the cohort; NSDUH is self-report; cannot control for all confounders at the individual level; causal inference methods applied to observational data have inherent limitations.
How to read the evidence
Moderate: very large sample with formal causal inference methods, but ecological design limits individual-level conclusions.
When this study was published
Published 2020.
The bigger picture
If the causal inference is correct, cannabis legalization may be contributing measurably to population-level mental health burden. The 12.91% attributable fraction for serious mental illness under legalization would have substantial public health implications.
Questions still open
- Do individual-level longitudinal studies confirm these population-level associations? Would cannabis policies that limit THC potency reduce mental health impacts?
Common questions
Does cannabis legalization increase mental illness?
Which mental health conditions are linked to cannabis?
Read the original research
Co-occurrence across time and space of drug- and cannabinoid- exposure and adverse mental health outcomes in the National Survey of Drug Use and Health: combined geotemporospatial and causal inference analysis.
BMC public health, 20(1), 1655
Citation
Reece, Albert Stuart; Hulse, Gary Kenneth. (2020). Co-occurrence across time and space of drug- and cannabinoid- exposure and adverse mental health outcomes in the National Survey of Drug Use and Health: combined geotemporospatial and causal inference analysis.. BMC public health, 20(1), 1655. https://doi.org/10.1186/s12889-020-09748-5
Explore the wider topic
- LGBTQ+ and Cannabis: Higher Use Rates and Recovery
- Cannabis-Induced Psychosis: What It Is, Who's at Risk, and What to Do
- BetterHelp, Cerebral, and Online Therapy: Honest Review
- Quitting Weed with ADHD: Why It Is Harder and What Actually Helps
- Quitting Weed with Depression: What You Need to Know
- Quitting Weed with PTSD: A Practical Guide
- Self-Medicating with Weed: Why It Works Until It Doesn't
- Weed and OCD: Self-Medicating Intrusive Thoughts
- Weed and PTSD: What the Research Actually Shows
- Weed and Childhood Trauma: ACEs, Self-Medication, and the Path to Real Healing
- Weed and Suicidal Thoughts: What You Need to Know