Yes, Flagyl (generic name: metronidazole) can change your urine to a dark or reddish-brown color during treatment, but this is not dangerous or very common.

• This pigment change is due to a metabolite of metronidazole that occurs when it's broken down in your body for elimination through your kidneys, so it's nothing to be concerned about.
• It's also very uncommon - instances of darkened urine have been reported by approximately one patient in 100,000.
• If you experience this side effect, your urine should change back to its normal color a day or two after you stop treatment. Normally, urine should look light yellow to nearly colorless.

It can be shocking to see your urine color change color when taking Flagyl, but this has been reported with other drugs, too. Many other medications -- including rifampin, sulfasalazine, and propofol -- can change the color of urine.

If your urine does not clear up to a normal color after you stop treatment, contact your doctor for further evaluation.

This is not all the information you need to know about Flagyl (metronidazole) for safe and effective use and does not take the place of your doctor’s directions. Review the full product information and discuss this information and any questions you have with your doctor or other health care provider.