What color is your poop when you are on antibiotics?

Why Your Poop Might Turn Green on Antibiotics

It’s not uncommon to notice changes in your stool when you’re on antibiotics — including a surprising shift in color. One of the more common changes? Green poop.

Antibiotics are designed to kill harmful bacteria, but they don’t discriminate — they can also wipe out beneficial gut microbes. These bacteria play a key role in digestion and help break down bile, a fluid produced by the liver that helps process fats. When your gut microbiome is disrupted, bile doesn’t get broken down as efficiently, and this can leave your stool with a greenish tint.

Another factor? Speed. Some antibiotics can speed up how quickly food moves through your digestive tract. When stool passes too quickly, bile doesn’t have enough time to undergo its normal chemical changes — which usually turn it from green to brown. The result? Green poop.

Generally, no. A temporary color change like this is usually harmless and resolves once your gut bacteria rebalance after finishing the antibiotic course. However, if the green color is accompanied by persistent diarrhea, severe cramping, fever, or blood in the stool, it’s best to consult a healthcare provider — these could be signs of a more serious imbalance, like a C. difficile infection.

Diet can also influence stool color — foods high in chlorophyll (like spinach) or green food coloring may contribute. But if you’re on antibiotics and notice green poop without eating a salad every day, the medication is likely the culprit.

Bottom line: Your gut is a complex ecosystem, and antibiotics can stir things up — sometimes in visible ways. Green poop might be strange, but it’s usually just a temporary side effect of your body adjusting.