New multi-site study presented at natural mental health It has been found that using cannabis and tobacco together increases the risk of developing psychiatric disorders such as schizophrenia, which are considered high-risk.
Researchers led by Heather Ward, M.D., assistant professor of psychiatry and behavioral sciences and director of neuromodulation research at Vanderbilt Health, analyzed data from more than 1,000 participants in the North American Progenitor Longitudinal Study, which tracks individuals at “clinical high risk” for psychosis. These people often experience mild or early symptoms but have not yet developed a full-blown psychotic disorder.
The prevalence of cannabis and tobacco use, known as “sharing,” has increased in the general population over the past few decades, while tobacco-only use has declined and cannabis-only use has increased. However, little is known about the combined use of cannabis and tobacco in adolescents at risk for psychosis. ”
Heather Ward, MD, assistant professor of psychiatry and behavioral sciences and director of neuromodulation research at Vanderbilt Health University
Drug use patterns (tobacco only, cannabis only, concomitant use, other drug use, no drug use) were assessed over a two-year period in 734 people at clinically high risk for psychosis and 278 healthy controls.
“People with mental illness are much more likely to use cannabis and tobacco than the general population. Because of their heavy use of cannabis and tobacco, people with mental illness are also disproportionately affected by the negative effects of cannabis and tobacco use,” said Dr. Ward, who recently presented the findings in an oral session titled “High-stakes: The Impact of Cannabis Use in Vulnerable Populations” at the Society of Biological Psychiatry’s annual meeting.
Dr. Ward said smoking in psychiatric patients reduces life expectancy by 20 years compared to the general population, and this is due to medical consequences of smoking such as cardiovascular disease, heart attacks, strokes and lung cancer.
“It is estimated that 25-50% of people who develop psychosis for the first time use cannabis. Cannabis use is associated with more severe psychotic symptoms, poor response to treatment, and psychiatric hospitalization. There is even evidence that cannabis use can precipitate psychosis in people who are already at risk,” Ward said.
“Tobacco and cannabis use alone have devastating effects on people with mental illness, so we wanted to find out whether people who use cannabis and tobacco together have more severe psychotic symptoms, or are at higher risk of developing psychosis in the first place.”
The study found that regular use of cannabis or tobacco was associated with anxiety, depression, and early psychotic experiences. However, those who used marijuana and tobacco together had no worse short-term symptoms than those who used only one or the other.
The biggest differences emerged over time. People who used cannabis frequently and used tobacco lightly were almost three times more likely to develop psychosis than those who did not use either substance.
The results highlight concerns about joint use, a previously understudied but growing trend. The researchers defined joint use in this study as “the use of substances at the same time, on the same occasion, or within a defined time frame whose effects may overlap.”
“We found that the combination of cannabis and tobacco use was associated with a nearly three-fold increased risk of developing psychosis in people who were already at risk,” Ward said. “There is evidence to suggest that using tobacco and cannabis together may have synergistic effects on the brain.
“Smoking tobacco and cannabis together increases the absorption of THC, the psychoactive component of cannabis. It is possible that the sharing itself contributes to the development of psychosis. However, it is also possible that people who are on the verge of developing psychosis anyway have an underlying predisposition to use both cannabis and tobacco.”
Ward said it’s important for both patients and clinicians to know that the combination of cannabis and tobacco use is a risk factor for psychosis. Stopping cannabis and tobacco use may improve mental health symptoms, and stopping cannabis and tobacco use may reduce the risk of developing psychosis in the first place.
The next step is to replicate this finding in other groups of people at risk for psychosis, and “will need to test whether cessation of cannabis and tobacco use reduces the risk of developing psychotic disorders,” Ward said.
sauce:
Vanderbilt University Medical Center
Reference magazines:
Bello, D. Others. (2026). Cannabis and tobacco use predicts psychosis in a clinically high-risk cohort. natural mental health. DOI: 10.1038/s44220-026-00648-y. https://www.nature.com/articles/s44220-026-00648-y
