When a 46-year-old man was pulled over for suspected drunk driving, officers figured it would be an open-and-shut case. A test revealed a blood alcohol level of 0.2, well past the legal limit, and the man’s claims that he didn’t ingest even a drop of alcohol seemed like a poor excuse. As it turns out, he was telling the truth.

The man’s unusual condition, called auto-brewery syndrome, causes his stomach to produce its own alcohol. The case was described in a new report which explains that an extended regimen of antibiotics was likely responsible for a dramatic shift in the many’s stomach chemistry.

Getting drunk without drinking sounds like something you’d see in a Saturday Night Live sketch, but the reality was no laughing matter for the man. After three weeks on antibiotics, the man began experiencing a wide range of symptoms that you’d normally associate with having one too many cocktails, including “brain fog,” depression, and aggression.

A family member had heard of auto-brewery syndrome before and urged the man to contact a specialist. Subsequent testing showed that the man’s blood-alcohol level spiked after eating a carb-heavy meal, so he was told to avoid carbs entirely. This helped for a while but eventually, the symptoms returned. One of his “drunken” episodes resulted in a fall and a serious head injury, leading him to seek medical help once again.

Further testing revealed unusual fungal growth in the man’s gut. Antifungal therapy was administered, eventually accompanied by a probiotic, and that seemed to do the trick. Now, a year and a half later, he remains free of symptoms and is believed to be back to normal.

In the case report, the authors suggest that the condition is likely more prevalent than anyone realizes:

ABS is probably an underdiagnosed condition. We believe that our patient’s symptoms were triggered by exposure to antibiotics, which resulted in a change in his gastrointestinal microbiome allowing fungal overgrowth.

The doctors believe that carbohydrate testing should be done on patients with a history of elevated blood-alcohol levels who insist they did not consume alcohol prior to the testing.