Some People Get Drunk Without Drinking and Scientists Finally Know Why

A hidden army of gut microbes can brew alcohol inside the body—and scientists may finally know how to stop it.

Scientists have identified specific gut bacteria and biological pathways that cause alcohol to be produced inside the body in people with auto-brewery syndrome (ABS). This rare and frequently misunderstood condition causes individuals to become intoxicated even though they have not consumed alcohol. The study was led by researchers at Mass General Brigham, working with collaborators from the University of California, San Diego, and was published today (January 7) in Nature Microbiology.

How Auto-Brewery Syndrome Works

Auto-brewery syndrome develops when certain gut microbes break down carbohydrates and convert them into ethanol (alcohol), which then enters the bloodstream. Small amounts of alcohol can be produced during normal digestion in anyone, but in people with ABS, these levels can rise high enough to cause noticeable intoxication. Although the condition is extremely rare, researchers believe it is often overlooked because many clinicians are unfamiliar with it, testing is difficult, and social stigma may discourage proper evaluation.

Years of Misdiagnosis and Serious Consequences

People with ABS frequently go years without an accurate diagnosis. During that time, they may face social isolation, medical complications, and even legal trouble due to unexplained intoxication. Confirming the condition is challenging because the gold standard diagnostic method requires carefully supervised blood alcohol testing over time, which is not widely available.

Comparing Patients, Partners, and Healthy Controls

To better understand what drives the disorder, researchers studied 22 people diagnosed with ABS, 21 of their unaffected household partners, and 22 healthy control participants. The team analyzed and compared the makeup and activity of gut microbes across all three groups.

When stool samples collected during active ABS flare-ups were tested in the laboratory, samples from patients produced much higher levels of ethanol than samples from partners or healthy controls. This finding suggests that stool-based testing could one day help doctors diagnose the condition more easily and accurately.

Identifying the Microbes Behind ABS

Until now, scientists had limited insight into which specific microbes were responsible for auto-brewery syndrome. Detailed stool analysis revealed that several bacterial species appear to play a key role, including Escherichia coli and Klebsiella pneumoniae. During symptom flare-ups, some patients also showed sharply elevated levels of enzymes involved in fermentation pathways compared to control participants. The researchers note that while these organisms were identified in some patients, pinpointing the exact causative microbes in each individual remains a complex and time-consuming process.

Fecal Transplant Offers Clues to Treatment

The research team also closely monitored one patient whose symptoms improved after receiving a fecal microbiota transplantation when other treatments had failed. Periods of relapse and remission closely matched changes in specific bacterial strains and metabolic activity in the gut, strengthening the biological evidence behind the diagnosis. After a second fecal transplant, which included a different antibiotic pretreatment, the patient remained symptom-free for more than 16 months.

Hope for Better Diagnosis and Care

“Auto-brewery syndrome is a misunderstood condition with few tests and treatments. Our study demonstrates the potential for fecal transplantation,” said co-senior author Elizabeth Hohmann, MD, of the Infectious Disease Division in the Mass General Brigham Department of Medicine. “More broadly, by determining the specific bacteria and microbial pathways responsible, our findings may lead the way toward easier diagnosis, better treatments, and an improved quality of life for individuals living with this rare condition.”

Hohmann is currently working with colleagues at UC San Diego on a study evaluating fecal transplantation in eight patients with ABS.

Reference: “Gut microbial ethanol metabolism contributes to auto-brewery syndrome in an observational cohort” by Cynthia L. Hsu, Shikha Shukla, Linton Freund, Annie C. Chou, Yongqiang Yang, Ryan Bruellman, Fernanda Raya Tonetti, Noemí Cabré, Susan Mayo, Hyun Gyu Lim, Valeria Magallan, Barbara J. Cordell, Sonja Lang, Münevver Demir, Peter Stärkel, Cristina Llorente, Bernhard O. Palsson, Chitra Mandyam, Brigid S. Boland, Elizabeth Hohmann and Bernd Schnabl, 8 January 2026, Nature Microbiology.
DOI: 10.1038/s41564-025-02225-y

Authorship: In addition to Hohmann, Mass General Brigham authors include Valeria Magallan. Additional authors include Cynthia L. Hsu, Shikha Shukla, Linton Freund, Annie C. Chou, Yongqiang Yang, Ryan Bruellman, Fernanda Raya Tonetti, Noemí Cabré, Susan Mayo, Hyun Gyu Lim, Barbara J. Cordell, Sonja Lang, Peter Stärkel, Cristina Llorente, Bernhard O. Palsson, Chitra Mandyam, Brigid S. Boland, Elizabeth Hohmann, and Bernd Schnabl.

Disclosures: Schnabl has been consulting for Ambys Medicines, Boehringer Ingelheim, Ferring Research Institute, Gelesis, HOST Therabiomics, Intercept Pharmaceuticals, Mabwell Therapeutics, Patara Pharmaceuticals, Surrozen and Takeda. Schnabl’s institution UC San Diego has received research support from Axial Biotherapeutics, BiomX, CymaBay Therapeutics, Intercept, NGM Biopharmaceuticals, Prodigy Biotech and Synlogic Operating Company. Schnabel is founder of Nterica Bio. Hohman has received research support from Seres Therapeutics, MicrobiomeX/Tend.

Funding: This work was supported by the National Institutes of Health (grants K99 AA031328 and T32 DK007202), the American Association for the Study of Liver Diseases Foundation (Grant #CTORA23-208366), and a Pilot and Feasibility Award from the Southern California Research Center for ALPD and Cirrhosis funded by the National Institute on Alcohol Abuse and Alcoholism of the National Institutes of Health P50AA011999 (to C.L.H), in part by NIH grants R01 AA024726, R01 AA020703, U01 AA026939, by Award Number BX004594 from the Biomedical Laboratory Research & Development Service of the VA Office of Research and Development (to B.S.) and services provided by NIH centers P50 AA011999 and the San Diego Digestive Diseases Research Center (SDDRC) P30 DK120515. This study was supported in part by NIH grants R01 AA029106, 1R21 AA030654, P30 AR073761 the D34 HP31027 UC San Diego’s Hispanic Center of Excellence, and by the Isenberg Endowed Fellowship jointly awarded by the Pilot/Feasibility Program of the San Diego Digestive Diseases Research Center (SDDRC), the Hellman Family Foundation (P30 DK120515) (to C.L.). This work was also supported by the Joint BioEnergy Institute, U.S. Department of Energy, Office of Science, Biological and Environmental Research Program under Award Number DE-AC02-05CH11231. This publication includes data generated at the UC San Diego IGM Genomics Center utilizing an Illumina NovaSeq X Plus that was purchased with funding from a National Institutes of Health SIG grant (#S10 OD026929).

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