Imagine blowing a dangerously high number on a breathalyzer without having had a drink in weeks. This episode explains auto-brewery syndrome, also called gut fermentation syndrome, in which yeasts such as Saccharomyces cerevisiae, the same species used by bakers and brewers, along with strains of Candida and some bacteria, colonize the gut and ferment carbohydrates into ethanol. Normally the liver’s alcohol dehydrogenase clears the trace alcohol digestion produces. In this condition production overwhelms it, and patients have been recorded with blood alcohol levels of 200 to 500 milligrams per deciliter.

Heavy antibiotic use can wipe out the gut’s bacteria while leaving yeast untouched, and conditions such as type 2 diabetes, liver cirrhosis, Crohn’s disease and short bowel syndrome raise the risk. Patients face disbelief from spouses and doctors until a locked down 24 hour carbohydrate challenge proves the alcohol is homemade. The episode also covers a bladder version seen in uncontrolled diabetes, the condition’s use as a drunk driving defense, and treatment with very low carbohydrate diets, antifungals such as fluconazole and nystatin, probiotics and fecal microbiota transplants.

• French physician Charles Bouchard wrote about intestinal fermentation and auto-intoxication in 1887
• A 1948 case in Uganda: a five year old boy whose stomach ruptured after yeast fermented the sweet potatoes he had eaten
• In urinary auto-brewery syndrome the patient stays sober while the urine itself turns alcoholic, in one report continuing to ferment in the collection cup
• A 25 year old man in 2019 who blew 0.3 with no drinks recovered on three weeks of daily fluconazole
• Mark Mongeardo documented his fight with the condition on TikTok in 2025