What are the Side Effects of Flagyl?

This article gives an overview on the common and serious side effects of Flagyl (metronidazole). Important information that everyone should know in using Flagyl are also provided.

Flagyl (Metronidazole) Information

Flagyl is an antibiotic drug used to treat infections caused by anaerobic bacteria and protozoa. Bacterial infections that uses Flagyl for treatment include bacterial vaginosis,  pelvic inflammatory disease, peritonitis, empyema, pneumonia, diabetic foot ulcer, meningitis, lung and brain abscesses, septicemia, endometritis, endocarditis, pseudomembranous colitis, peptic ulcer disease and among others. The most common protozoal infection where Flagyl is used for treatment is amebiasis.

The generic name for Flagyl is metronidazole, which belong to a group of drug called nitroimidazole. Once absorbed by bacterial and protozoan cells, metronidazole initiates the production of toxic compounds that would eventually kill the microorganisms. Flagyl is marketed by Pfizer in the US, globally by Sanofi-Aventis, and various generic manufacturers. It is available in capsules and extended-release tablets.

Common and Severe Side Effects of Flagyl

As with any medication, Flagyl may cause side effects. However, there are some who can tolerate the side effects quite well.  If side effects do occur, in most cases, they are minor and either require no treatment or can easily be treated by you or your doctor.

Below is the list of common Flagyl side effects. Note that the list is not complete and you may experience other side effects. Check with your doctor if the side effects persist or become bothersome to you.

  • Nausea
  • Vomiting
  • Headache
  • Stomach upset
  • Diarrhea
  • Constipation
  • Loss of appetite
  • Unpleasant metallic taste in the mouth
  • Cough
  • Sneezing
  • Runny nose


The serious side effects of Flagyl are listed below. You should seek medical attention right away if you experience them. Note that the following list of severe Flagyl side effects is not complete; you may experience other side effects that should be reported immediately to your doctor.

  • Severe allergic reactions such as hives, rashes, itching, shortness of breath, and swelling of the lips, mouth, face, or tongue.
  • Severe diarrhea (watery and bloody)
  • Severe or persistent headache
  • Sore throat
  • Chills
  • Fever
  • Speech problems
  • Stiff neck
  • Severe stomach pain or cramps
  • Vaginal itching, discharge, or unusual odor
  • Loss of vision or other vision changes
  • Loss of balance
  • Increased or decreased urination
  • Burning pain when urinating
  • Seizures or convulsions
  • White patches in the mouth or lips
  • Numbness or tingling in the hands or feet

Precautions in Using Flagyl

  • Do not drink alcohol while taking Flagyl. Flagyl and alcohol mixing is known to have bad reactions to the body such as fast heartbeats (trachycardia), flushing in the skin, nausea, vomiting, and tingly feeling.
  • Do not take Flagyl if you are allergic to any of its ingredients.
  • Before taking Flagyl, tell your doctor if you have liver disease, nerve disorders, epilepsy or other seizure disorders, blood cell diseases like anemia, and stomach or intestinal disease like Crohn’s disease.
  • Do not take Flagyl if you are breastfeeding because it was shown that the drug can pass onto the breast milk and may harm your baby.
  • If you missed a dose, take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take extra dose to make up the missed one.
  • Read and follow the directions as written on your prescription label. Ask your doctor or pharmacist, if there is anything you can’t understand in the label. Do not take Flagyl at a larger dose, take it more often, or for a longer period other than your doctor tells you to.


The information in this article is not a substitute for professional medical advice. Please seek advice from your doctor before taking any action suggested on this article.[ad#afterpost]