Researchers at the University of California, San Diego, Mass General Brigham, and their colleagues have identified specific gut bacteria and metabolic pathways that drive alcohol production in patients with auto-brewery syndrome (ABS). The rare and often misunderstood condition causes people to experience intoxication without drinking alcohol. The study was published in Nature Microbiology on January 8, 2026.
ABS occurs when gut microbes break down carbohydrates and turn them into ethanol (the alcohol found in alcoholic beverages), which then enters the bloodstream. While carbohydrate metabolism can produce small amounts of alcohol in everyone, the levels can be high enough to cause intoxication in people with ABS. The condition is extremely rare but possibly underdiagnosed due to lack of awareness, diagnostic challenges and stigma.
Medical consequences of ABS can include liver damage, cognitive impairment, digestive problems, and withdrawal symptoms, among others. Many patients experience chronic misdiagnosis and social, medical, and legal consequences before receiving a diagnosis. Confirmation of ABS is also difficult to achieve, as the gold standard diagnosis requires monitoring of the blood alcohol test under supervised conditions.
In the largest study of the condition to date, researchers evaluated 22 patients with ABS, 21 unaffected domestic partners and 22 healthy control participants, comparing gut microbial composition and function between the groups.
They found that stool samples taken from patients during an ABS flare produced significantly more ethanol than samples from household partners and healthy controls.
Previously, scientists had very little information about which specific gut microbes (yeasts or bacteria) caused ABS. Stool analysis showed several bacterial species as key drivers in some patients.
“We found that gut bacteria, incl Escherichia coli and Klebsiella pneumoniaeferment sugars into ethanol in the gut in patients with ABS,” said Bernd Schnabl, MD, professor of medicine at the UC San Diego School of Medicine. “These microbes use several pathways to produce ethanol and can drive blood alcohol levels high enough to cause legal intoxication.”
While some patients had these organisms, the authors note that identifying the exact microbes responsible for ABS in individual patients is difficult. However, during ABS flares, some patients also had significantly higher levels of enzymes involved in fermentation pathways compared to controls. The authors note that rather than focusing on specific species of bacteria, therapies that target microbial enzymes involved in ethanol production may be a more effective strategy.
The results also suggest that a stool-based test could serve as an alternative to follow-up blood alcohol testing for the diagnosis of ABS, leading to faster and more accessible screening.
The researchers also followed a patient who experienced relief of symptoms after receiving a fecal microbe transplant when other treatments had failed. Patterns of relapse and remission corresponded with changes in specific bacterial strains and metabolic pathway activity, providing further biological clues to the condition. After a second stool transplant, the patient was symptom-free for more than 16 months.
Auto-brewery syndrome is a misunderstood condition with few tests and treatments. Our study demonstrates the feasibility of faecal transplantation. More generally, by identifying the specific bacteria and microbial pathways responsible, our findings may lead to easier diagnosis, better treatments and improved quality of life for people living with this rare condition.”
Elizabeth Hohmann, MD, co-senior author, Division of Infectious Diseases, Brigham Department of General Medicine
Schnabl, Hohmann and colleagues are currently conducting a phase 1 clinical trial evaluating fecal microbiota transplantation in eight patients with ABS. They believe studies like this could also have lessons for treating other conditions, such as liver disease associated with metabolic dysfunction.
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