Oral bacteria enriched in chronic cannabis smokers caused anxiety-like behavior in mice when introduced into their mouths, working through metabolites that impair mitochondria and GABA signaling in the brain without bacteria actually reaching the brain.
Researchers interested in the gut-brain axis, oral microbiome, and cannabis-anxiety connections.
Oral bacteria metabolites reached the brain and caused anxiety in mice
What the researchers found
Actinomyces species, previously found to be enriched in chronic cannabis smokers' oral microbiome, induced anxiety-like behaviors in mice when inoculated orally. The bacteria produced metabolites (arginine and argininosuccinate) that increased in both oral swabs and brain tissue, causing mitochondrial dysfunction, oxidative stress, and reduced GABAergic neurotransmission. Notably, the bacteria themselves did not travel to the brain; their metabolites did.
Why it matters
This is a novel oral-brain axis discovery. It suggests that some anxiety associated with chronic cannabis use might not be caused by cannabinoids directly but by changes in oral bacteria that cannabis smoking promotes. This opens an entirely new avenue for understanding cannabis-related neuropsychiatric effects.
The numbers in context
A. meyeri showed strongest effects. Increased arginine and argininosuccinate in oral swabs and brain. Microglia activation without classical neuroinflammation (no IL-1 beta, TNF-alpha, or IL-6 increase). Reduced GABAergic neurotransmission. No memory decline observed.
How the study worked
Wild-type C57BL/6 mice received oral inoculation with cannabis use-associated Actinomyces species. Behavioral testing assessed anxiety. Brain analysis measured microglia activation, mitochondrial function, and GABA signaling. In vitro experiments tested Actinomyces-produced metabolites on neurons.
What this study cannot tell us
Animal study with bacterial inoculation, not natural cannabis use. Preprint (not yet peer-reviewed). Cannot determine if findings apply to human cannabis users. Single bacterial genus tested. Cannot distinguish cannabis-specific effects from general oral microbiome effects.
How to read the evidence
Preliminary: novel animal study with detailed mechanistic work, but preprint status and uncertain human relevance.
When this study was published
Published as preprint in 2025.
The bigger picture
The oral-brain metabolic axis is an emerging concept. This study suggests that cannabis's effects on mental health may extend beyond direct cannabinoid actions to include microbiome-mediated pathways. If confirmed in humans, it could explain some of the variability in cannabis-anxiety relationships.
Questions still open
- Do chronic cannabis smokers have elevated Actinomyces-derived metabolites in their brains?
- Could oral hygiene interventions reduce cannabis-associated anxiety?
- Does this oral-brain pathway contribute to anxiety in human cannabis users?
Common questions
Can cannabis change your oral bacteria?
Could oral bacteria explain cannabis-related anxiety?
Read the original research
Cannabis-enriched oral Actinomyces induces anxiety-like behavior via impairing mitochondria and GABA signaling.
bioRxiv : the preprint server for biology
Citation
Salman, Tabinda; Luo, Zhenwu; Johnson, Douglas; Noorani, Arshad A; Wan, Zhuang; Bordieanu, Bogdan; Ye, Zhi-Wei; Penrod, Rachel D; Xian, Hongxu; Fitting, Sylvia; Kalivas, Peter W; Jiang, Wei. (2025). Cannabis-enriched oral Actinomyces induces anxiety-like behavior via impairing mitochondria and GABA signaling.. bioRxiv : the preprint server for biology. https://doi.org/10.1101/2025.11.21.689724
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