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This New Study Will Test Marijuana’s Effect on Oral Bacteria

By Leo Bear-McGuinness

Published: Jan 16, 2023   
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Researchers from North and South Carolina will soon begin the first known study to investigate how cannabis affects oral bacteria and the brain.

The researchers – from the Medical University of South Carolina and the University of North Carolina at Chapel Hill – plan to first expose mice to different levels of THC and CBD. They hypothesize that long-term exposure to THC (but not CBD) will increase the amount of Actinomyces meyeri bacteria in the mice’s saliva, an increase that could lead to “harmful neurological” effects.  


After the stomach, the human mouth houses the most diverse community of microbes found in the body. Over 700 species of bacteria can typically be found living on a person’s tongue, teeth, and oral tissue.

Several studies have already demonstrated that cigarette smoke can upset this fragile ecosystem, but much less is known about the effects of cannabis smoke.

One of the few researchers investigating this cannabis-mouth health relationship is Wei Jiang, a professor of microbiology and immunology at the Medical University of South Carolina.

In 2021, she and her colleagues tested the oral microbiomes of 16 cannabis smokers and 27 non-smokers. They found that the cannabis smokers had abnormally high levels of Actinomyces meyeri bacteria in their mouths. This finding raised some concerns, as the presence of A. meyeri has been associated with the development of neurodegenerative diseases, such as Alzheimer’s and dementia.

“In general, the amount of A. meyeri should be very low in a healthy oral microbiome,” Jiang said in a statement.

To investigate further, Jiang and her colleague Dr. Sylvia Fitting of the University of North Carolina at Chapel Hill proposed their upcoming study.

After they conduct their mice experiments, the two researchers then plan to study the mouths of human participants diagnosed with cannabis use disorder, to see whether changes in their oral bacteria have affected their memory.

“We expect memory-related deficits to be associated with greater levels of A. meyeri in frequent cannabis users compared with nonusers,” Jiang said.

To fund their study, Jiang and Fitting secured a $3.7 million grant from the National Institute on Drug Abuse (NIDA).

With this NIDA funding in hand, Jiang is hopeful her research can lay a foundation for developing diagnostic tests that could identify the oral microbiomes in frequent cannabis consumers that may portend to future neurological disorders.

“If our hypothesis is correct, a therapeutic strategy targeting A. meyeri could reduce irregularities in brain function in frequent cannabis users,” said Jiang. “In the future, it may also be useful to screen for certain bacteria as biomarkers of different diseases that affect the brain, such as Alzheimer’s disease.”


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