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Cannabis and Tobacco Co-Use Predicts Psychosis in Clinical High Risk Cohorts
Daniel Bello1, Sophia H Blyth1, Rachel A Rabin2
1Department of Psychiatry and Behavioral Sciences, Vanderbilt University Medical Center.
Medrxiv : the Preprint Server for Health Sciences
|September 26, 2025
Summary
Concurrent cannabis and tobacco use significantly increases the risk of developing psychosis in individuals at clinical high risk (CHR). Early interventions addressing this co-use are crucial for mitigating long-term psychiatric outcomes.
Area of Science:
- Psychiatry
- Neuroscience
- Public Health
Background:
- Cannabis and tobacco use are common in individuals with psychosis, linked to poor health outcomes.
- Concurrent use, or co-use, is increasing but understudied in psychosis risk populations.
- Understanding co-use impact is critical for psychosis prevention and management.
Purpose of the Study:
- To investigate the association between cannabis and tobacco co-use and psychiatric symptoms.
- To examine the risk of conversion to psychosis in individuals with varying substance use patterns.
- To compare outcomes across clinical high risk (CHR) for psychosis groups and healthy controls.
Main Methods:
- Prospective, multi-site study (North American Prodrome Longitudinal Study 2) of 1,014 participants (734 CHR, 280 controls).
- Categorized participants into distinct substance use groups (tobacco, cannabis, co-use, other, none).
- Utilized survival analyses to assess conversion to psychosis risk.
Main Results:
- More frequent cannabis and tobacco use correlated with higher psychiatric symptom severity (psychosis, anxiety, depression).
- Co-use, particularly heavy co-use, significantly increased the risk of conversion to psychosis (HR=2.53 for co-use, HR=3.63 for heavy co-use).
- Co-use predicted psychosis conversion risk independently of psychiatric symptom severity.
Conclusions:
- Concurrent cannabis and tobacco use poses a significant, potentially synergistic, risk for psychosis development in CHR individuals.
- Co-use may serve as a marker for heightened underlying psychosis vulnerability.
- Early intervention strategies targeting co-use in CHR populations are essential to prevent severe psychiatric consequences.
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