Cannabis and Tobacco Co-Use Dramatically Raises Psychosis Risk in High-Risk Populations

By Dr. Natalie Singh, Health Editor

Published May 13, 2026

A groundbreaking study published in Nature Mental Health reveals that concurrent use of cannabis and tobacco—commonly referred to as “co-use”—significantly increases the risk of developing psychosis among individuals already at clinical high risk (CHR) for the disorder. The findings, drawn from the largest prospective study of its kind, underscore the urgent need for targeted interventions in vulnerable populations.

Key Findings: Co-Use Doubles Psychosis Conversion Risk

The North American Prodrome Longitudinal Study-2 (NAPLS-2), a multisite investigation involving 1,012 participants (734 CHR individuals and 278 healthy controls), found that:

Heavy cannabis and light tobacco co-use was associated with a 2.93-fold increased risk of transitioning to psychosis compared to no substance use (95% confidence interval: 1.23–6.97, P = 0.015) [1].
While cannabis and tobacco use individually were linked to greater psychiatric symptom severity, co-use specifically predicted higher conversion rates to psychosis, regardless of symptom baseline.
Up to 62% of individuals with schizophrenia use tobacco—a prevalence three times higher than the general population, according to prior research [1].

These results challenge previous assumptions that cannabis or tobacco use alone drives psychosis risk, instead highlighting the synergistic danger of co-use.

Why Does Co-Use Increase Psychosis Risk?

Experts suggest several biological and behavioral mechanisms may explain the heightened risk:

Increased Psychosis Risk Study

Neurochemical Synergy: Both substances affect dopamine pathways—cannabis by overstimulating CB1 receptors and tobacco by triggering nicotine-induced dopamine release. This dual disruption may accelerate psychotic symptom onset in predisposed individuals.
Shared Risk Factors: Individuals with CHR traits often self-medicate with cannabis or tobacco to cope with anxiety, sleep disturbances, or cognitive dysfunction—both of which are early psychosis markers.
Addiction Vulnerability: Co-use may exacerbate substance use disorders, creating a feedback loop that worsens psychiatric instability.

Dr. John McGrath, a study co-author and psychiatrist at the University of Queensland, notes: *”The interaction between these substances isn’t just additive—it’s multiplicative. Clinicians must screen for co-use in CHR patients and provide harm-reduction strategies early.”* [1]

Who Is Most Affected?

The study identified three high-risk groups where co-use poses the greatest danger:

Young Adults (16–25): The peak age for first-episode psychosis coincides with the highest rates of cannabis and tobacco experimentation.

Individuals with Family History: Those with a first-degree relative diagnosed with schizophrenia or bipolar disorder face a 10% lifetime risk of psychosis—a risk amplified by co-use [1].

Mental Health Service Users: Patients already engaging with psychiatric care for depression, anxiety, or trauma are 4x more likely to co-use substances.

What Should Clinicians and Patients Do?

The study’s authors emphasize preventive and therapeutic actions:

Screening: Routine assessment for cannabis and tobacco use in CHR clinics, using validated tools like the Cannabis Use Disorders Identification Test (CUDIT).
Harm Reduction: For those unable to quit, reducing frequency (e.g., switching from daily to weekly use) may lower risk.
Behavioral Interventions: Cognitive behavioral therapy (CBT) tailored to substance use has shown promise in reducing psychosis relapse rates.
Policy Changes: Public health campaigns should target dual-use messaging, not just cannabis or tobacco in isolation.

FAQ: Addressing Common Questions

1. Does this mean cannabis or tobacco alone are safe?

No. While co-use poses the highest risk, individual use of either substance is also linked to poorer psychiatric outcomes, including symptom exacerbation and treatment nonadherence [1].

2. Are there any benefits to cannabis for mental health?

Current evidence does not support cannabis as a therapeutic tool for psychosis prevention. In fact, THC—the psychoactive compound in cannabis—has been shown to trigger psychotic episodes in vulnerable individuals, particularly at high doses [2].

3. How can families support at-risk loved ones?

Encourage open conversations about substance use without judgment.
Provide access to non-judgmental support groups, such as those offered by the National Alliance on Mental Illness (NAMI).
Monitor for early warning signs of psychosis (e.g., social withdrawal, paranoia, hallucinations) and seek professional evaluation promptly.

Looking Ahead: Research and Policy Gaps

While the study provides critical insights, experts highlight areas needing further exploration:

Long-Term Outcomes: How does co-use impact functional recovery and quality of life years after psychosis onset?
Alternative Therapies: Are there non-pharmacological interventions (e.g., mindfulness, exercise) that can mitigate co-use risks?
Global Disparities: How do co-use patterns vary across cultures, and do risk factors differ in regions with higher vs. Lower cannabis/tobacco accessibility?

The findings serve as a wake-up call for public health efforts. As cannabis legalization expands and tobacco use persists as a global epidemic, the intersection of these substances demands immediate attention—particularly in populations already vulnerable to psychosis.

Key Takeaways

Co-use of cannabis and tobacco nearly triples the risk of psychosis in high-risk individuals.

Screening for co-use should be standard practice in psychiatric care.

Harm reduction strategies can lower risk even if quitting isn’t possible.

Families and clinicians must act early to prevent substance-driven psychotic episodes.

Dr. Natalie Singh is a board-certified internal medicine physician and health editor specializing in evidence-based mental health reporting. Her work has been featured in JAMA Psychiatry and The Lancet.

References

Cannabis and Tobacco Co-use Linked to Increased Psychosis Risk