There is a medical condition, albeit rarely diagnosed, in which an individual experiences the effects of alcohol without actually ingesting alcohol. This condition, known as auto-brewery syndrome (ABS) (46), results from the endogenous production of ethanol through the fermentation of carbohydrates by microbes in the gastrointestinal system, oral cavity, and/or urinary tract (47–49). Individuals with ABS often have gastrointestinal disorders, such as Crohn’s disease, or a history of antibiotic overuse, both of which can alter the microbiome, allowing fungal or bacterial overgrowth and potentially contributing to the development of this condition (50–52). For example, ABS has been linked to the presence of yeast strains such as Saccharomyces cerevisiae, S. boulardii, Candida spp., and rare bacteria like Klebsiella pneumoniae, Enterococcus faecium, and Citrobacter freundii (53–55). While endogenous ethanol production is known to cause slight elevations in BAC, there is debate over whether ABS alone can cause BAC elevations to levels above 0.8 grams per liter of blood (g/L; equivalent to 0.08% BAC), which is the legal limit for driving in the U.S. and therefore could have clinical or forensic significance (6, 56).
