Why do I get gassy on antibiotics?

Your gut is a fermentation factory run by trillions of bacteria, and antibiotics do not aim - they hit the infection and take collateral. When an antibiotic thins out parts of your gut bacterial community, digestion reshuffles: some carbohydrates that used to be handled quietly now get fermented by whichever bacteria remain, and that fermentation produces gas. The NHS lists stomach pain, diarrhoea, and feeling or being sick among the common side effects of antibiotics, and MedlinePlus confirms antibiotics can have side effects - a gassy, rumbly, bloated week is the ordinary version of that story. It typically starts a few days into the course and settles within days to a couple of weeks after the last pill, as your gut community rebuilds. What helps: take the antibiotic exactly as directed (with food if the label allows - it cushions the stomach), eat simply and lightly during the course, go easy on the gas-heaviest foods for a few days (beans, fizzy drinks, rich fatty meals), and finish the full course even though your stomach is complaining - stopping early is how resistant infections happen. The line that matters: severe, watery, or bloody diarrhoea during or after antibiotics is not gas - MedlinePlus warns antibiotics can trigger C. diff infections that damage the colon, so that pattern needs a same-day call to your prescriber, especially with fever or bad cramps. Ordinary bloat just needs patience. Pymander is a free AI doctor, 24/7 by text, that can help you judge where yours sits.