A new study published in Nature Mental Health examines how cannabis and tobacco use influence the risk of developing psychosis in individuals with elevated vulnerability. Researchers followed more than one thousand people identified as being at clinical high risk and analyzed how different consumption patterns affected long-term outcomes.
The results show that combined use of cannabis and tobacco was associated with a significantly higher risk of transitioning to psychosis compared to individuals who used neither substance. The group using both substances also displayed more pronounced psychiatric symptoms during the follow-up period.
Combined Use Stands Out
The most striking finding was that individuals who used both cannabis and tobacco had the highest likelihood of progressing from a high-risk state to a formal psychosis diagnosis. The effect remained even after researchers adjusted for factors such as age, gender, and socioeconomic background.
This suggests that the interaction between the substances may play a critical role, rather than cannabis exposure alone.
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Cannabis Without Tobacco
When researchers isolated cannabis use without concurrent tobacco consumption, a more nuanced pattern emerged. The association between cannabis alone and transition to psychosis was weaker than in the combined-use group, but not entirely absent.
Previous research has shown that frequent use and products with high THC content may increase the likelihood of psychotic symptoms, particularly among young people and individuals with genetic or psychological vulnerability.
Possible Biological Mechanisms
Nicotine and THC affect the brain’s signaling systems in different but partially overlapping ways. Nicotine can enhance dopamine activity, which is central in the development of psychotic disorders. THC influences the endocannabinoid system, which regulates several neurochemical processes.
The combination may therefore create an amplified neurobiological effect that increases vulnerability in already at-risk individuals.
Implications for Prevention and Care
The researchers emphasize that the findings do not demonstrate a direct causal relationship. The study identifies statistical associations between patterns of use and increased risk, but it cannot prove that substance use itself causes psychosis. Other underlying factors may contribute to the observed outcomes, even though multiple known risk variables were controlled for.
Overall, the study contributes to a more detailed understanding of how different consumption patterns relate to mental health risk and highlights the importance of distinguishing between cannabis-only use and combined use in both research and public health discussions.
Source
Cannabis and tobacco co-use predicts psychosis in clinical high risk cohorts
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