For years, cannabis and tobacco have often been discussed as two separate health risks. But new research suggests that using them together could have particularly serious consequences for the brain—especially in people already vulnerable to psychosis.
A major study published in Nature Mental Health in May 2026 found that people considered clinically at high risk for psychosis who frequently used cannabis alongside tobacco had a substantially greater chance of progressing to a full psychotic disorder.
The most striking finding involved heavy cannabis use combined with tobacco use, which was associated with almost a threefold greater risk of developing psychosis compared with using neither substance.
While this does not mean that everyone who smokes cannabis and tobacco will develop schizophrenia, the findings raise important questions about how the two substances may interact in vulnerable brains.
What Did the Study Find?
Researchers examined data from the North American Prodrome Longitudinal Study-2, a large project involving people considered at clinical high risk for psychosis, along with healthy control participants.
The analysis included more than 1,000 participants.
Researchers divided them according to their patterns of cannabis and tobacco use and followed them to determine who later developed psychosis.
The study found that using cannabis and tobacco together predicted a greater likelihood of progressing to psychosis than avoiding both substances.
Most notably, heavy cannabis use combined with light tobacco use was associated with a hazard ratio of 2.93—meaning the rate of progression to psychosis was nearly three times higher than among those who used neither substance.
The researchers emphasized that the findings do not prove that the combination directly causes psychosis. Co-use could potentially intensify biological effects, or it may identify individuals who already have other risk factors.
Still, the association was strong enough to warrant attention.
Psychosis and Schizophrenia Are Not Exactly the Same Thing
Headlines about studies like this sometimes use the terms “psychosis” and “schizophrenia” interchangeably, but they are not identical.
Psychosis describes a state in which a person’s perception of reality becomes disrupted.
Symptoms can include:
- hallucinations
- delusions
- confused or disorganized thinking
- paranoia
- difficulty distinguishing reality from internal experiences
Schizophrenia is a specific psychiatric disorder in which psychosis can be a major feature.
A person can experience psychosis without having schizophrenia. Psychotic episodes can also occur in bipolar disorder, severe depression, substance-induced conditions, and several other illnesses.
The 2026 study specifically measured progression to psychosis, so describing the result as a guaranteed threefold increase in schizophrenia risk would be an oversimplification.
Why Cannabis Has Long Been Linked to Psychosis
Cannabis contains dozens of biologically active compounds, but the one most closely associated with intoxication and psychotic symptoms is tetrahydrocannabinol, or THC.
THC interacts with the body’s endocannabinoid system, which plays a role in mood, memory, cognition, reward signaling, and stress responses.
For many people, cannabis produces temporary relaxation or altered perception.
For others—particularly at high doses—it may trigger anxiety, paranoia, unusual thoughts, or hallucination-like experiences.
Research has repeatedly found that frequent cannabis use, especially involving high-THC products, is associated with greater risk of psychotic disorders.
The relationship appears particularly concerning among adolescents and young adults, whose brains are still developing.
Recent research has also suggested that adolescence may represent an especially vulnerable window. A Canadian study discussed at an international early-psychosis meeting found a strong association between adolescent cannabis use and later health-care contact for psychotic disorders.
Where Does Tobacco Fit In?
Tobacco has traditionally been associated primarily with lung cancer, cardiovascular disease, COPD, and other physical illnesses.
But nicotine also acts directly on the brain.
It influences neurotransmitters including dopamine, which plays an important role in reward, motivation, learning—and psychosis.
Tobacco smoking is unusually common among people with schizophrenia and other psychotic disorders.
The authors of the 2026 study noted that as many as 62% of people with schizophrenia use tobacco, far higher than rates seen in the general population.
Researchers have debated why this association exists.
Some people may smoke nicotine in an attempt to temporarily relieve cognitive or emotional symptoms. Shared genetic, social, and environmental factors may also contribute.
However, growing evidence suggests tobacco itself may not be completely neutral when it comes to psychosis risk.
Could Cannabis and Nicotine Amplify Each Other?
This is one of the most intriguing questions raised by the new study.
Cannabis and nicotine influence overlapping brain systems.
Both can modify dopamine signaling, reward pathways, attention, stress responses, and neural plasticity.
Researchers therefore suspect that using the two substances together could produce effects different from using either one alone.
In the 2026 study, cannabis-only and tobacco-only groups did not show statistically significant increases in conversion to psychosis when compared with non-users in the categorical analysis.
The combined-use group did.
That pattern raises the possibility of a synergistic effect, meaning the combination could potentially affect the brain more strongly than either substance independently.
However, researchers caution that another explanation is possible: people who use both substances heavily may simply represent a group with greater underlying vulnerability.
More research is needed to separate these possibilities.
Today’s Cannabis Is Not the Cannabis of Decades Past
Another issue researchers increasingly emphasize is cannabis potency.
Modern cannabis products can contain far more THC than products commonly used decades ago.
Concentrates, vape cartridges, oils, and certain flower varieties may deliver very high THC doses in a short period.
This matters because psychosis risk appears to rise with heavier and more potent cannabis exposure.
Frequent use also matters.
People who use cannabis daily or nearly every day may experience very different neurological exposure than someone who uses it occasionally.
For someone with a family or personal vulnerability to psychosis, that distinction could be especially important.
Who May Be Most Vulnerable?
Psychosis usually develops from a combination of influences rather than a single cause.
Possible risk factors include:
Family history. Having a close relative with schizophrenia or another psychotic disorder can increase vulnerability.
Adolescence and young adulthood. Many psychotic disorders first appear during these years.
Heavy or high-potency cannabis use. Frequent exposure to strong THC products appears particularly concerning.
Previous unusual experiences. Persistent paranoia, hallucinations, severe suspiciousness, or major changes in thinking should not be ignored.
Sleep deprivation and severe stress. These may worsen symptoms in vulnerable people.
Multiple substance use. Combining cannabis with tobacco, stimulants, hallucinogens, or other drugs may complicate neurological effects.
Having one or even several risk factors does not mean a person will develop schizophrenia. Mental illness results from complicated interactions between biology and environment.
Early Warning Signs Should Be Taken Seriously
Psychosis rarely looks exactly the same from one person to another.
Early changes may include growing suspiciousness, social withdrawal, declining performance at school or work, difficulty organizing thoughts, unusual beliefs, changes in sleep, or hearing or seeing things that others do not.
Some people may also feel that ordinary events contain hidden messages specifically intended for them.
These experiences warrant professional evaluation, particularly if they are persistent or worsening.
Early intervention programs for psychosis have become an important part of modern psychiatric care because treatment during the earliest stages can improve long-term outcomes.
What About People Who Already Use Cannabis and Tobacco?
The purpose of research like this is not to stigmatize people who use cannabis or nicotine.
Instead, it provides information that can help people make more informed decisions.
For someone who has experienced paranoia, hallucinations, severe anxiety after cannabis, or other psychosis-like symptoms, continuing heavy cannabis use may carry particular risks.
The same applies to people who have been told they are at clinical high risk for psychosis.
Reducing or stopping cannabis and tobacco use may therefore become part of a broader mental-health strategy under medical supervision.
Nicotine dependence can be difficult to overcome, and quitting abruptly may produce withdrawal symptoms. Evidence-based smoking cessation programs, behavioral therapy, nicotine-replacement strategies, and medical support can help.
The Bigger Message
The cannabis conversation has changed dramatically in recent years.
As legalization and social acceptance have expanded in many countries, cannabis is increasingly viewed as relatively harmless.
But “natural” does not automatically mean risk-free.
The effects of cannabis depend on dose, frequency, THC concentration, age, individual genetics, mental-health history, and whether other substances are being used at the same time.
The new Nature Mental Health research adds another important factor:
tobacco co-use.
Among people already clinically vulnerable to psychosis, heavy cannabis use combined with tobacco was associated with nearly triple the risk of progressing to psychosis.
That does not mean cannabis and tobacco automatically cause schizophrenia.
But it does suggest that the combination deserves much more attention—particularly among teenagers, young adults, and people already showing warning signs of psychosis.
As researchers continue to unravel the connection between cannabis, nicotine, brain chemistry, and psychiatric illness, one message is becoming increasingly difficult to ignore:
what substances are combined may matter just as much as how much of each substance is used.
