Metronidazole side effects & how to manage them

Metronidazole’s side effects most commonly involve the gastrointestinal tract and include nausea, a headache, or stomach upset.

Not everyone experiences side effects from Metronidazole. If they do, these side effects tend to be mild and resolve on their own once the treatment is finished. Listed below are some of Metronidazole's side effects:

Gastrointestinal (GI)

If you experience GI side effects such as nausea or vomiting while taking this medicine, try taking it with food or a snack. This can help reduce stomach irritation and nausea.

Stick to simple meals and avoid spicy foods or foods high in fat or fibre, as they may worsen stomach upset. Try to identify and avoid foods or drinks that may trigger nausea, such as strong odours and alcohol.

If you're vomiting or experiencing diarrhoea, try to avoid becoming dehydrated by drinking water throughout the day. Drink small sips of water or electrolytes often instead of drinking a lot at once. This can help you feel better if you are feeling unwell.

Signs of dehydration to look out for include peeing less than usual or having dark, strong-smelling pee.

If you vomit or have diarrhoea while taking birth control pills, they may not work as well to prevent pregnancy. This is because they might not be absorbed properly. Consult your pill information leaflet for advice.

Headache

If you experience a headache while taking this medicine, try taking a break and resting in a quiet place. You can also ask a healthcare professional about taking over-the-counter pain relievers to help relieve the headache. Sometimes dehydration can contribute to headaches, so drink plenty of water when taking Flagyl.

Metallic taste

Some people may experience a sharp or unpleasant metallic taste in their mouth when taking this medication. Here are some tips for combating this feeling:

• Drink water or suck on ice chips throughout the day to keep your mouth moist.
• Chew sugar-free gum or suck on sugar-free candies, especially those with strong flavours like mint or citrus. This can help mask the metallic taste.
• Rinse your mouth with alcohol-free mouthwash or a saline solution a few times a day.

If your tongue feels furry, this could be a sign of thrush – ask your pharmacist or doctor for advice.

Metronidazole’s serious side effects are very rare but may include:

Neurological

Studies have shown that in rare cases, metronidazole may cause neurological side effects such as seizures, nerve damage, or encephalopathy (brain disease). This is more likely to occur if the medicine is used for long periods of time or at high doses.

Contact your healthcare provider if you develop symptoms like seizures, numbness or tingling in the hands or feet, confusion, hallucinations, changes in vision or a stiff neck.

Blood disorders

Flagyl can rarely cause changes in blood cell counts, leading to:

• A low white blood cell count
• A low platelet count
• A low levels of red blood cells

Signs of blood disorders may include unusual bruising or bleeding, fever, unexpected infections, mouth ulcers, or severe tiredness.

If you experience any of these serious side effects while taking Flagyl, seek immediate medical attention. Flagyl may also affect the results of some blood tests.

Liver problems

This medication may rarely cause liver toxicity, cholestatic or mixed hepatitis, or an increase in liver enzymes. Signs of liver problems may include jaundice (yellowing of the skin or eyes), dark urine, abdominal pain, or ongoing nausea and vomiting. Report these symptoms to your doctor immediately.

Allergic reactions

Some people may experience allergic reactions to antibiotics, like Flagyl. Symptoms of allergic reactions may include rash, itching, swelling of the face, tongue, or throat, severe dizziness, or trouble breathing. Seek immediate medical attention if you experience any of these symptoms.

You should not drink any alcoholic beverages while you are taking this antibiotic and for 48 hours after finishing the course of treatment.

Drinking alcohol with Metronidazole might cause side effects such as nausea, vomiting, headache, stomach pain, hot flashes, or a very fast heartbeat.

Some side effects may be more common depending on which application form of Metronidazole you use. While we've discussed side effects mainly related to Metronidazole tablets (Flagyl), here are some specific to other forms of Metronidazole.

Vaginal gel

Metronidazole gel (Zidoval) can cause side effects that are specific to the vaginal area and may include:

• redness of the skin
• vaginal itching or irritation
• skin discomfort (burning, pain of skin/stinging)
• vaginal thrush
• vaginal discharge
• discomfort around your pelvis or abdomen
• a burning sensation when you pee

Topical creams and gel

Up to 1 in 10 people may experience side effects when Metronidazole creams or gels (Acea, Anabact, Metrogel, Metrosa, Rosiced, Rozex) are applied to the skin. Here are the most common side effects reported:

• dry skin or redness
• skin irritation (an itching, burning, or stinging sensation)
• worsening of rosacea

Other side effects may include numbness and tingling in the fingers or toes, a metallic taste in the mouth, and nausea. However, these are uncommon and may only affect up to 1 in 100 people.

If you experience side effects with one form of metronidazole, such as oral tablets, you may be able to switch to a different form, if it’s appropriate. However, it's important to speak to your healthcare provider before making any changes to your medication regimen. Your doctor can guide you to transition between forms of metronidazole safely.

Most side effects from this medication shouldn’t last long. The length of time you experience side effects will vary depending on your body's individual response to the medication. Each person may react to the same medication in different ways.

Usually, side effects may start soon after you take a tablet, and should resolve within several hours to a few days, depending on the type of side effect you experience.

When should I speak to a healthcare professional?

If you have been taking Metronidazole and you are concerned that the side effects you are experiencing are unusual, then you should report these side effects to your doctor.

You may need to stop the treatment or switch to an alternative, but it is best to talk to your doctor before doing so.

Read more about Metronidazole here