metronidazole (Flagyl) Side Effects and Adverse Effects

  • Pharmacy Author:
    Omudhome Ogbru, PharmD

    Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.

What is metronidazole (Flagyl, Flagyl ER)?

Brand name(s): Flagyl, Flagyl ER

Metronidazole (Flagyl, Flagyl ER) is a prescription antibiotic available as tablet, extended release tablet, capsule, lotion, gel, and injection form prescribed to treat a variety of parasitic and bacterial infections, for example:

Common side effects are loss of appetite, headaches, and nausea. Serious side effects are encephalopathy, seizures, and aseptic meningitis. Metronidazole may be taken with or without food.


Avoid drinking alcohol while taking this drug because the combination can cause severe nausea, vomiting, headache, flushing, and cramps. Drug interactions, and pregnancy and breastfeeding safety information should be reviewed prior to taking Flagyl. Ask your doctor or pharmacist if you have questions about this drug.

If you notice other effects not listed above, contact your doctor or pharmacist. In the US -Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the entire consumer metronidazole (Flagyl) drug information >>

What are the side effects of metronidazole (Flagyl)?

Flagyl is a useful antibiotic and is generally well tolerated with appropriate use.

The most common and minor side effects include:

Side effects that are uncomfortable, but may become serious include:

  • Brain disease
  • Fevers
  • Mouth sores
  • Pain with urination
  • Prickling or tingling sensations that may become permanent
  • Cystitis
  • Pelvic pain or pressure
  • Decrease of libido
  • Proctitis
  • Stomitis
  • Glossitis

Serious side effects of Flagyl are rare and the drug should be stopped if these symptoms appear:

If you notice other effects not listed above, contact your doctor or pharmacist. In the US -Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Read the entire consumer metronidazole (Flagyl) drug information >>

Medically Reviewed by a Doctor on 5/16/2017

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