Short answer
Yes. Antibiotics disturb the bacteria in your gut, which can cause loose stool that looks green or yellow. It usually settles after the course ends. Watery diarrhea three or more times a day, cramping, fever or blood, during antibiotics or in the weeks after, can be C. difficile infection and needs medical advice.
Why do antibiotics change stool?
Antibiotics can change stool because they kill helpful gut bacteria as well as harmful ones. That changes how food is broken down and how fast it moves, and can cause loose stool. Faster transit can leave bile green, and stool can look green or yellow.
Which stool changes on antibiotics are usual, and which are not?
Mildly loose stool that looks green or yellow is a common side effect of antibiotics. Frequent watery diarrhea, fever or blood is not a usual side effect and needs medical advice.
| What you see | What it usually means |
|---|---|
| Soft or loose stool, green or yellow | Common and usually mild. Often settles in days after finishing the course. |
| Red stool in an infant on cefdinir | A reported effect with iron-fortified formula. Always mention it to the pediatrician. |
| Watery diarrhea, three or more times a day, with cramps or fever | Could be C. difficile. See a doctor. |
| Bloody diarrhea | Needs medical attention. |
| Black, tarry stool | Not an antibiotic effect. Get care. See black stool. |
What is C. diff (C. difficile infection), and how is it different?
C. difficile (C. diff) can overgrow when antibiotics reduce the normal gut bacteria. It causes watery diarrhea, belly cramps, fever and loss of appetite, and can be severe. It can start during antibiotics or in the weeks after. It needs testing and treatment, and often a different antibiotic.
Things to discuss with your doctor or pharmacist
- Do not stop or change a prescribed antibiotic without asking your doctor or pharmacist.
- How to stay hydrated if stool is loose.
- How to take your medicine. Always follow the label and your prescriber's instructions.
- Whether any other product, such as a probiotic, is suitable for you. Do not start one without advice.
- Whether anti-diarrhea medicine is suitable. It may not be, especially with fever or blood in stool.
When should you see a doctor about diarrhea on antibiotics?
Contact a doctor about three or more watery stools a day, diarrhea lasting more than two days, or diarrhea that starts after finishing antibiotics. Bloody diarrhea or severe belly pain needs care right away.
Usually harmless
- Mildly loose, green or yellow stool during the course, and you feel well
Call a doctor within a day
- Diarrhea lasting more than two days, or three or more watery stools a day
- Diarrhea that starts in the weeks after you finish antibiotics
- Cramping or fever
Get care now
- Bloody diarrhea, severe belly pain, or a swollen belly
- Signs of dehydration
- A baby or young child with watery diarrhea and fewer wet diapers
Warning signs to know
These are signs that published medical guidance says need prompt or urgent care. The list is not complete, and ticking boxes cannot tell you whether you are ill. If you are worried, contact a clinician whatever you tick.
Questions people ask
Can antibiotics make poop yellow or green?
Yes. They can cause loose stool, and faster transit can leave stool green or yellow.
How long does diarrhea last after antibiotics?
Mild cases usually settle within days after finishing the course. If it lasts longer or is severe, see a doctor.
Is C. diff the same as normal antibiotic diarrhea?
No. Ordinary antibiotic diarrhea is usually mild. C. diff causes frequent, watery diarrhea with cramps and sometimes fever, and needs treatment.
Should I stop my antibiotic if I get diarrhea?
Do not stop without advice. Call your doctor or pharmacist, who can tell you whether to change treatment.
Sources
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