Cannabis and Tobacco Co-Use May Increase Psychosis Risk

Key Takeaways

• • A new study in Nature Mental Health found that cannabis and tobacco co-use may significantly increase psychosis risk in individuals already considered clinically high risk.
  • Researchers analyzed data from more than 1,000 participants in the North American Prodrome Longitudinal Study.
  • Heavy cannabis use combined with light tobacco use was linked to nearly a threefold increase in psychosis development.
  • Co-use was also associated with anxiety, depression, and early psychotic symptoms.
  • Investigators say clinicians should monitor cannabis and tobacco use patterns in vulnerable adolescents and young adults.

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Cannabis and Tobacco Co-Use Linked to Higher Psychosis Risk

A new multicenter study published in Nature Mental Health reports that cannabis and tobacco co-use may substantially increase the likelihood of developing psychotic disorders, including schizophrenia, among individuals already considered at clinical high risk for psychosis.

Researchers led by Heather Ward from Vanderbilt Health evaluated substance use trends in participants enrolled in the North American Prodrome Longitudinal Study, a large research initiative focused on identifying early markers of psychotic disorders.

The study assessed 734 individuals at clinical high risk for psychosis and 278 healthy controls over two years. Investigators categorized participants based on substance use patterns, including cannabis only, tobacco only, cannabis and tobacco co-use, other substances, or no substance use.

Researchers noted that cannabis and tobacco co-use has steadily increased over the last several decades, especially among adolescents and young adults. While exclusive tobacco use has declined, cannabis consumption continues to rise, creating concern among psychiatric specialists about long-term neuropsychiatric outcomes.

How Cannabis and Tobacco Co-Use Affects Mental Health

The study found that both cannabis use and tobacco use independently correlated with anxiety, depressive symptoms, and early psychotic experiences. However, the most significant findings emerged in participants who regularly used both substances together.

Patients with heavy cannabis use and lighter tobacco use demonstrated nearly three times the risk of progressing to psychosis compared with participants who avoided both substances.

According to Ward, people with psychotic disorders already experience disproportionately high rates of cannabis and tobacco exposure. Tobacco-related cardiovascular disease, stroke, lung cancer, and other medical complications contribute to significantly reduced life expectancy in this population.

Investigators also highlighted evidence suggesting that tobacco may increase absorption of tetrahydrocannabinol (THC), the psychoactive component of cannabis. This interaction could intensify neurobiological effects associated with psychosis vulnerability.

Why Clinicians Should Monitor Substance Co-Use in At-Risk Youth

The findings emphasize the importance of early screening for cannabis and tobacco co-use in adolescents and young adults presenting with mild psychotic symptoms or psychiatric vulnerability.

Researchers believe co-use may either directly contribute to psychosis development or reflect an underlying biological predisposition among individuals already susceptible to psychiatric illness.

Ward emphasized that reducing or discontinuing cannabis and tobacco use may improve psychiatric outcomes and potentially lower psychosis risk in vulnerable populations. The research team plans to conduct additional studies to determine whether smoking cessation and cannabis abstinence can prevent progression to full psychotic disorders.

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For psychiatrists, primary care clinicians, nurses, and behavioral health professionals, the study reinforces the need for targeted counseling on substance use in high-risk populations. It highlights the growing psychiatric concerns surrounding cannabis and tobacco co-use.

Source:

Vanderbilt University Medical Center