Scientists tracked what actually happens inside the gut after antibiotics. Their findings challenge one of the most common pieces of recovery advice.

For years, the advice was simple: finish your antibiotics, take a probiotic, move on. Doctors said it, pharmacists said it, the label on the packet practically implied it. The problem is that the research on what actually happens inside the gut after a course of antibiotics tells a considerably more complicated story.

In 2018, researchers at the Weizmann Institute of Science in Israel did something most probiotic studies had never done. Instead of measuring stool samples, they examined the gut mucosa directly, using endoscopy to look at what was happening at the intestinal lining, where recolonization actually matters. What they found about the popular multi-strain probiotic supplements most people reach for after antibiotics was not what anyone expected.