Skip to content

Metronidazole (Flagyl)

What is it?

Metronidazole is an antibacterial-antiprotozoal medicine used to treat different bacterial and parasitic infections.

How to take this medication:

Metronidazole should be taken after a meal to avoid stomach upset. Antibiotics work best when the amount of medicine in your body is kept at a constant level. If you need to take more than one dose, be sure to evenly space out the doses (ex: 7am and 7pm). It is important to take this medication until it is gone, even if symptoms go away after a few days. Stopping the medication too early may allow bacteria to keep growing.

Do NOT take this medication if you:

Are allergic to metronidazole (Flagyl).

Are allergic to nitroimidazoles (ex. Tinidazole).

Are allergic to any of the non-medicinal ingredients.

Have an active neurological condition or a disease of the nervous system.

Have a history of blood disease.

Have hypothyroidism or hypoadrenalism.

Tell your health care provider if you:

Are pregnant or breastfeeding.

Have liver problems.

Are taking corticosteroids (may cause sodium retention).

Side effects:

Some people may experience the following common side effects:

  • Upset stomach, stomach pain, nausea, or loss of appetite
  • Vomiting or diarrhea
  • Furry tongue
  • Buzzing or ringing in the ears
  • Change in taste (metallic taste)
  • Sleepiness
  • Dark urine (red-brown colour)

Repeated or long term use of this medication may cause yeast infections in women.

Do not drive or operate machinery if you experience any of the following rare symptoms:

  • Confusion
  • Dizziness
  • Hallucinations
  • Seizure

Tell your health care provider if you develop numbness, tingling, pain or weakness in your arms or legs.

Allergic reactions to this medication are rare, but these reactions can be very serious if not treated right away. If you experience any of the following symptoms, seek medical attention right away:

  • Trouble breathing
  • Swelling in the face, mouth and neck
  • Severe skin rash, hives or blisters

Drug interactions:

Tell your health care provider about any medications you take. Your dose may need to be adjusted or changed. Drugs that can interact with metronidazole include:

  • Alcohol
  • Busulfan (Myleran)
  • Cyclosporine (Neoral)
  • Disulfiram
  • 5-fluorouracil (5-FU)
  • Lithium
  • Blood thinners
  • Phenytoin (Dilantin)
  • Phenobarbital

Missed dose:

If you miss a dose, take it as soon as you remember. However, if it is almost time for the next dose, do not take the missed dose and take the next dose as scheduled. Do not take a double dose to make up for a forgotten dose.


Store tablets at room temperature. Do not allow medication to freeze. Keep out of reach and sight of children.

Points to remember:

AVOID all alcoholic beverages while taking this medication and for at least 24 hours after treatment is complete as severe stomach pain, vomiting, hot flushes, very fast or uneven heartbeat and headache can occur.