Cannabis smoking linked to oral bacteria that caused brain changes in mice

Cannabis smokers showed oral microbial dysbiosis with increased Streptococcus and Actinomyces and decreased Neisseria. Mice orally exposed to the cannabis-enriched bacterium Actinomyces meyeri for six months showed decreased global activity, increased macrophage brain infiltration, and increased beta-amyloid 42 protein production.

Researchers compared saliva microbiomes of 16 chronic cannabis smokers with cannabis use disorder and 27 non-smoking controls using 16S rRNA sequencing. Then mice were orally inoculated with Actinomyces meyeri, Actinomyces odontolyticus, or Neisseria elongata twice weekly for six months to test functional effects.

This is the first study to connect cannabis-associated changes in oral bacteria to potential neurological consequences, suggesting a novel pathway by which chronic cannabis smoking might affect brain health.

The oral microbiome-brain axis is an emerging area of research. This study adds cannabis smoking as a factor that may reshape oral bacteria in ways that have downstream neurological consequences, though the pathway from human observation to mouse experiment needs further validation.

Very small human sample (16 vs 27). Mouse model may not replicate human oral-brain pathways. Cannot determine whether cannabis itself or combustion byproducts caused the microbial changes. No control for tobacco co-use.