Do antibiotics cause diarrhea because of "bad bacteria?"

Reviewed by Yoshinori Abe, MD

Internal Medicine

Antibiotic-associated diarrhea occurs when antibiotics disrupt the natural balance of bacteria in your gut. While antibiotics target harmful bacteria causing infection, they also kill beneficial bacteria that aid digestion. This imbalance allows harmful bacteria, such as C. difficile, to overgrow, leading to loose stools, cramping, and bloating. Symptoms typically appear within a week of starting antibiotics and may persist after treatment ends.

Not sure if your diarrhea is a normal side effect or something more serious? Understanding your symptoms early can help you decide whether to continue your medication, contact your doctor, or seek urgent care. Take a free, instant, online symptom check to get personalized insights based on your specific situation and clear guidance on your next steps.

Reviewed for medical accuracy: 07/15/2026

Important Next Steps

Learn if antibiotics are causing diarrhea Discover what may be causing your diarrhea See if bad bacteria need treatment Find OTC relief for diarrhea symptoms Find a doctor for diarrhea concerns Learn medically valid home remedies for diarrhea Understand if diarrhea needs urgent care

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Explanation

Antibiotics are medicines that kill bacteria causing infections, but they can also affect the good bacteria in your gut. When this happens, it can lead to diarrhea.

How It Happens:

Good vs. Bad Bacteria: Your gut is home to many bacteria, both good and bad. Antibiotics can kill off some of the good bacteria that help keep your gut healthy.
Growth of Bad Bacteria: With fewer good bacteria, bad bacteria like Clostridium difficile can grow more easily. This can cause diarrhea.

Other Bacteria:

Besides Clostridium difficile, other bacteria might also cause diarrhea when the balance in the gut is upset.

In summary, while antibiotics are important for treating infections, they can sometimes cause diarrhea by disturbing the natural balance of bacteria in the gut. If you're experiencing digestive issues or other concerning symptoms, you can check your symptoms to better understand what might be happening.

(References)

Varughese CA, Vakil NH, & Phillips KM. (2013). Antibiotic-associated diarrhea: a refresher on causes and .... Journal of pharmacy practice, 24064436.
Capurso L, & Koch M. (2021). [Side effects of antibiotic: diarrhea and Clostridium difficile .... Recenti progressi in medicina, 33576348.
Song HJ, Shim KN, Jung SA, Choi HJ, Lee MA, Ryu KH, et al. (2008). candidate organisms other than Clostridium difficile. The Korean journal of internal medicine, 18363274.

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