Cannabis, Tobacco, and Psychosis Risk: Clinical Implications for Therapists
Originally published: May 23, 2026 | Category: Clinical Research
Let us talk about a study that should change how you assess substance use in at-risk clients. Published in Nature Mental Health in May 2026, a multi-site prospective study led by Dr. Heather Ward at Vanderbilt University Medical Center examined the relationship between cannabis and tobacco co-use and psychosis transition risk in clinical high-risk populations. The findings are sobering and clinically actionable.
This is not just another study confirming that cannabis has risks. It is the first large-scale prospective analysis to demonstrate that the combination of cannabis and tobacco together creates a risk that is greater than the sum of its parts. For therapists working with adolescents and young adults, the implications are immediate and practical.
The Study: What They Found and Why It Matters
The research team used data from the North American Prodrome Longitudinal Study 2, analyzing 1,014 participants. Of these, 734 were at clinical high risk for psychosis and 280 were healthy controls. Participants were categorized into six groups based on substance use patterns: tobacco-only use, cannabis-only use, co-use of both cannabis and tobacco, other substance use, no substance use, and healthy controls. The study followed participants prospectively, tracking who transitioned to full psychosis over time.
The headline finding is stark: co-use of cannabis and tobacco was associated with a 2.53-fold increased risk of transitioning to psychosis. For heavy co-use, defined as daily or near-daily use of both substances, the risk jumped to 3.63-fold. To put this in perspective, that is comparable to the increased risk associated with having a first-degree relative with schizophrenia.
Key Findings at a Glance
| Substance Use Pattern | Hazard Ratio for Psychosis Transition | 95% CI | p-value |
|---|---|---|---|
| No substance use (CHR) | Reference | — | — |
| Tobacco-only use | 1.65 | 0.89–3.06 | 0.112 |
| Cannabis-only use | 1.89 | 1.02–3.51 | 0.044 |
| Cannabis + Tobacco co-use | 2.53 | 1.44–4.45 | 0.001 |
| Heavy co-use | 3.63 | 1.53–8.63 | 0.003 |
| Other substance use | 1.41 | 0.76–2.61 | 0.278 |
Source: Ward H, et al. Nature Mental Health. 2026. PMCID: PMC12458528
Importantly, co-use did not significantly predict higher psychiatric symptom severity scores compared to single-substance use, but it did predict conversion to psychosis. This dissociation between symptom severity and transition risk is clinically significant. It means you cannot rely on symptom monitoring alone to assess risk in clients who use both substances. The risk pathway appears to operate independently of observable symptom fluctuations.
Why This Matters for Your Practice
Here is the clinical reality: many of the clients you see, especially adolescents and young adults, are using both cannabis and tobacco. They may not even think of it as using tobacco because they are vaping nicotine rather than smoking cigarettes. But the neurobiological impact is similar, and the study specifically included all forms of tobacco and nicotine delivery.
Prevalence You Need to Know
- Up to 60 percent of people with schizophrenia use tobacco, three times the general population rate
- Current cannabis use disorders among people with psychosis: approximately 16 percent
- Lifetime cannabis use disorder among people with psychosis: approximately 27 percent
- Cannabis use is involved in roughly half of psychotic disorder cases in some populations
- Individuals who use cannabis have schizophrenia onset two to three years earlier than non-users
- Approximately 77 percent of individuals report using tobacco before the onset of psychotic symptoms
The Synergy Explained
Why does co-use amplify risk more than either substance alone? The study authors suggest several mechanisms supported by previous research:
- Pharmacokinetic interaction: Tobacco smoke accelerates the metabolism of THC through enzyme induction in the liver. This means people who smoke both cannabis and tobacco need to consume more cannabis to achieve the same effect, increasing overall THC exposure. It is a biological trap.
- Dopaminergic sensitization: Both nicotine and THC act on the mesolimbic dopamine pathway. Combined exposure may produce additive or synergistic dopamine dysregulation, which is the final common pathway for psychotic symptom development.
- Endocannabinoid system disruption: Chronic dual exposure may impair the brain’s natural protective mechanisms against psychotic symptoms. The endocannabinoid system normally acts as a brake on excessive dopamine signaling. When it is chronically disrupted by THC and nicotine simultaneously, that brake weakens.
- Behavioral reinforcement: The ritual of using both substances together creates strong conditioned associations that make cessation more difficult. Clients who co-use are less likely to successfully reduce either substance.
Clinical High Risk for Psychosis: What to Look For
If you work with adolescents and young adults, understanding the clinical high risk state is essential. The CHR designation is not a diagnosis. It is a research-based classification identifying individuals whose symptoms and functioning suggest they may be in the prodromal phase of a psychotic disorder. Here are the domains to monitor:
| Domain | Symptoms to Monitor | Example Presentation |
|---|---|---|
| Positive symptoms (attenuated) | Unusual thought content, suspiciousness, perceptual abnormalities | “I feel like people are watching me” or “Sounds seem louder and more meaningful than they should” |
| Negative symptoms | Social withdrawal, avolition, blunted affect | Dropping out of activities, declining grades, isolating in room for hours |
| Disorganized symptoms | Odd speech, bizarre behavior, poor hygiene | Tangential conversations, wearing inappropriate clothing, neglecting self-care routines |
| Functional decline | 30 percent or greater drop in functioning | Lost job, failing classes, relationship breakdowns, unable to maintain daily routine |
| Substance use change | Increased frequency or quantity of cannabis or tobacco | Moving from occasional to daily use, switching to higher-potency products, co-use emerging |
Screening for Substance Use in At-Risk Clients
If you work with adolescents, young adults, or clients with a family history of psychotic disorders, routine substance use screening is no longer optional. It is essential. Here is a practical screening protocol you can implement in your practice starting this week:
Step 1: Use Standardized Screening Tools
- CRAFFT 2.1: The gold standard for adolescent substance use screening. It takes two minutes and covers car, relax, alone, forget, friends, and trouble domains. Free and widely validated.
- DAST-10: The Drug Abuse Screening Test. Ten items covering broader substance use. Useful for adult clients as well.
- CAST: Cannabis Abuse Screening Test. Specifically validated for cannabis use. Six items that capture problematic use patterns.
Step 2: Ask About Co-Use Specifically
Do not just ask “Do you use cannabis?” or “Do you smoke or vape?” Ask: “Do you ever use cannabis and tobacco or vape products together?” Clients often do not volunteer this information because they do not realize it matters. Some may not even conceptualize their nicotine vape as tobacco use. Be specific: “When you vape THC, do you also vape nicotine? Do you mix them? Do you smoke blunts, which combine cannabis with tobacco wrappers?”
Step 3: Assess Frequency and Quantity
The study found clear dose-response relationships. More frequent use equals higher risk. Heavy use, defined as daily or near-daily use of both substances, was the strongest predictor. A detailed substance use history should include frequency, quantity, route of administration, product potency (THC percentage where available), and temporal relationship to symptom onset. Document this systematically so you can track changes over time.
Psychoeducation Strategies That Work
When you talk to clients about these findings, here is what resonates and what does not.
Use Normalizing Language
“A lot of people use cannabis to cope with stress or sleep issues. I understand why. What the latest research is showing is that when cannabis and nicotine are used together, there may be a stronger effect on the brain than either one alone. I want to make sure we are monitoring that together.” This approach reduces defensiveness and opens the door for honest conversation.
Focus on What They Care About
Young clients often care more about their goals than their symptoms. Frame it around what matters to them: “Using less might help you think more clearly in class.” “Your anxiety might actually improve if we look at the cannabis use together.” “If you want to keep your part-time job, cutting back on the combination could help with focus and attendance.”
Offer Alternatives Before Asking Them to Stop
If a client uses cannabis for anxiety or sleep, which many do, offer evidence-based alternatives before asking them to quit. CBT-I for sleep, exposure therapy for anxiety, behavioral activation for low motivation, and mindfulness-based stress reduction for emotional regulation. Give them something to replace it with. Asking someone to stop a coping mechanism without offering alternatives is rarely effective.
Address Blunt Use Specifically
Blunts, where cannabis is rolled in tobacco wraps, represent a particularly high-risk delivery method because they combine both substances in a single product. Clients who smoke blunts may not even realize they are co-using. Ask specifically about blunt use and provide targeted psychoeducation about the added risk.
When to Refer
If you identify a client who meets CHR criteria or even sub-threshold concerns and is using cannabis or tobacco, here is your referral roadmap:
- First-episode psychosis (FEP) clinic: Most major medical centers have specialized FEP programs designed for early intervention in prodromal or early psychosis. This is the gold standard referral for anyone showing attenuated positive symptoms.
- Coordinated Specialty Care (CSC): Programs like NAVIGATE combine medication management, psychotherapy, family education, and supported employment or education. Ideal for early psychosis.
- Addiction psychiatry: If substance use is heavy and the client is motivated to reduce or quit, a dual-diagnosis specialist can provide evidence-based treatment including motivational interviewing, contingency management, and pharmacotherapy for nicotine dependence.
- Psychiatric evaluation: For clients with emerging positive symptoms, a thorough diagnostic evaluation by a psychiatrist familiar with prodromal psychosis is essential. Do not wait for symptoms to become severe.
Practical Screening Protocol for Your Practice
| Step | Action | Frequency |
|---|---|---|
| 1 | Administer CRAFFT 2.1 or DAST-10 at intake | Initial session for all new clients under 30 |
| 2 | If positive, assess frequency, quantity, and co-use separately for cannabis and tobacco | Every session during active treatment |
| 3 | Monitor for CHR symptoms using PQ-B (Prodromal Questionnaire-Brief) | Quarterly if client uses substances regularly |
| 4 | Assess family history of psychotic disorders | Initial session and update if new information emerges |
| 5 | Provide psychoeducation on co-use risk using the Nature Mental Health data | When substance use is identified |
| 6 | Refer to FEP clinic if concerning symptoms emerge | Immediately |
What About Vaping?
This is the most common question I get from therapists. The short answer: yes, nicotine vaping counts as tobacco use for the purposes of this research. While the study focused primarily on combustible tobacco, the mechanisms of nicotine’s effect on psychosis risk are independent of the delivery method. If your client is vaping nicotine alongside cannabis, they are at similar risk as someone smoking both substances. The pharmacokinetic interaction (enzyme induction in the liver) may differ with vaping, but the dopaminergic effects are comparable. Do not let the delivery method obscure the risk.
Case Example: When Co-Use Shows Up in Session
Consider this common scenario. A 19-year-old college sophomore presents for therapy with complaints of anxiety and difficulty concentrating. They smoke cannabis most evenings to unwind and vape nicotine throughout the day. They do not think of themselves as a tobacco user because they are vaping. When asked about substance use at intake, they say “just a little weed sometimes.” They do not mention the nicotine vape because it feels incidental.
Their therapist, aware of the NAPLS-2 data, follows up: “Do you ever use cannabis and nicotine together?” The client pauses and says, “Yeah, actually. Most nights I’ll hit my weed pen and my vape at the same time.” This is co-use. This client has a family history of schizophrenia in a paternal uncle. They have been feeling increasingly suspicious that classmates are talking about them, though they acknowledge it might be “just anxiety.”
This client is exactly the population the Nature Mental Health study is describing: co-use in a vulnerable individual with emerging attenuated positive symptoms and a family history of psychotic disorder. The appropriate clinical response is not more anxiety management. It is a conversation about the co-use risk, a referral for psychiatric evaluation, and a discussion with a first-episode psychosis program. The therapist’s willingness to ask about co-use specifically is what made this identification possible.
The Role of Family History
Family history of psychotic disorders is one of the strongest predictors of psychosis risk and interacts with substance use in important ways. The combination of genetic vulnerability and cannabis exposure produces a risk that is greater than either factor alone. According to previous research, individuals with both a family history of psychosis and heavy cannabis use have an estimated four- to five-fold increased risk of developing a psychotic disorder compared to those with neither risk factor.
When you take a family history with your clients, ask specifically about psychotic disorders in first- and second-degree relatives, not just “mental illness” in general. Many clients do not know the specifics of their family psychiatric history, but you can ask them to check with family members. For clients who have both a positive family history and cannabis or co-use, the risk conversation should be explicit and detailed.
The goal is not prohibition. It is harm reduction through informed decision-making based on the best available evidence. This is not about scaring clients away from cannabis entirely. It is about informed consent. If a young person chooses to use cannabis despite knowing their family history and the associated risks, that is their choice. But they deserve to know what the data say before making that choice.
The Bottom Line
Cannabis and tobacco co-use is not just two bad habits. It is a distinct risk factor for psychosis transition in vulnerable individuals. The Nature Mental Health study provides the strongest evidence to date that the combination exerts a synergistic effect on psychosis risk that exceeds either substance alone.
As a therapist, you are often the first clinician to hear about a client’s substance use patterns. You are positioned to screen, educate, and refer. Do not underestimate the impact of a well-timed conversation about co-use. It could change the trajectory of a young person’s mental health. The data are clear: the combination matters more than either substance alone, and your willingness to ask about co-use specifically could identify a risk factor that would otherwise go unnoticed.
References:
- Ward H, et al. Cannabis and Tobacco Co-Use Predicts Psychosis in Clinical High Risk Cohorts. Nature Mental Health. 2026. PMCID: PMC12458528
- Di Forti M, et al. The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe. Lancet Psychiatry. 2019;6(5):427-436.
- Hartz SM, et al. Comorbidity of Severe Psychotic Disorders With Measures of Substance Use. JAMA Psychiatry. 2014;71(3):248-254.
- Addington J, et al. North American Prodrome Longitudinal Study (NAPLS 2): Overview and recruitment. Schizophr Res. 2012;142(1-3):77-82.
Integrating This Into Your Practice
The most important takeaway from this study is practical and immediate. When you take a substance use history from an adolescent or young adult client, you need to ask about cannabis and tobacco or nicotine use separately and together. Document the frequency and quantity of each substance individually and note when they are used together. Track this over time as part of your ongoing assessment. If you identify a client who uses both substances and has either a family history of psychosis or emerging attenuated symptoms, refer for specialized assessment promptly. The combination of co-use and vulnerability is the highest-risk scenario, and early intervention can be genuinely preventative.
This article is for educational purposes and does not constitute medical advice. Clinicians should consult the full study and relevant clinical guidelines before making treatment decisions.