Flagyl Side Effects

by on January 14, 2012


The side effects of Flagyl (metronidazole) are typically mild and very manageable. The most common include abdominal discomfort, nausea, diarrhea or constipation, headaches and dizziness. Darkening of the urine has been reported with Flagyl as well, but is not a cause for concern. More serious Flagyl side effects to be aware of include seizures, numbness, paralysis, mood and behavior changes and changes in vision. Though rare, these side effects are dangerous and should be reported to a healthcare provider immediately.

Common Flagyl Side Effects

Common side effects of Flagyl are typically mild. The majority of patients are able to manage their side effects successfully and do not need to stop taking the medication. They include the following:

  • Dizziness
  • Nausea
  • Stomach pain
  • Diarrhea
  • Vaginal discharge
  • Vaginal itching
  • Painful menstrual periods
  • Bacterial infections
  • Urinary tract infections
  • Sore or swollen tongue
  • Changes in taste
  • Metallic taste in the mouth
  • Dry mouth
  • Sneezing and running or stuffy nose
  • Cough
  • Sore throat
  • Sinus infection
  • Headache
  • Constipation
  • Loss of appetite
  • Flu-like symptoms
  • Darkening of the urine

These side effects are generally manageable for the duration of the regimen. However, if you experience persistent side effects that are difficult to manage or disrupt your daily routine, you should contact your healthcare professional. Do not stop taking Flagyl on your own as your underlying infection may return without adequate treatment.

Serious Flagyl Side Effects


Some individuals may experience an allergic reaction to Flagyl. If you are allergic to other nitroimidazoles like tinidazole, you may be allergic to Flagyl as well. Tell your doctor about these allergies before beginning a metronidazole medication. Side effects that may indicate an allergic reaction include:

  • Rash or hives
  • Difficulty breathing
  • Tightness of the chest
  • Itching
  • Swelling of the nose or throat

Other serious side effects of Flagyl that you should talk to your doctor about include the following:

  • Numbness in the arms, legs, hands or feet
  • Paralysis in any of the extremities
  • Seizures
  • White patches on the lips or mouth
  • Bloody or watery diarrhea
  • Flu-like symptoms such as fever, headache, sore throat, muscle pain and stiffness, nausea, vomiting and chills
  • Problems with vision
  • Difficulty concentrating
  • Unexplained changes in mood or behavior
  • Severe skin reaction including burning, blistering or peeling
  • Unusual bruising or bleeding

Flagyl side effects are rarely significant enough to cause the patient to stop taking the medication. As this is a short-term treatment, minor side effects are typically manageable. Some may even go away as your body adjusts to the drug. It is important to note that taking Flagyl and similar antibiotic medications too often can decrease the potency of these treatments. Always finish your regimen completely to avoid a relapse of the infection and the need to start a new dose.