Metronidazole Oral Tablet | Side Effects, Dosage, Uses & More
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Generic Name:

metronidazole, Oral tablet

All Brands

  • Flagyl
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Highlights for metronidazole

Oral tablet
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Metronidazole comes in the form of a capsule and tablet you take by mouth. It also comes as a cream, gel, and lotion you apply to your skin, and a vaginal gel. It’s also available as a self-injectable drug.

2

Metronidazole oral tablets are used to treat infections caused by bacteria or parasites. The tablets come in immediate-release and extended-release versions.

3

Metronidazole oral tablets are available as the brand-name drugs Flagyl (immediate-release) and Flagyl ER (extended-release). The immediate-release tablet is also available as a generic drug The extended-release tablet is not.

4

The more common side effects of the oral tablets include headache, loss of appetite, vomiting, diarrhea, or heartburn.

5

In some cases, the oral tablets can cause serious side effects. These include seizures or other nervous system disorders.

IMPORTANT INFORMATION

FDA warning

Metronidazole oral tablets and capsules have a black box warning. This is the most serious warning from the Food and Drug Administration (FDA). A black box warning alerts doctors and patients about drug effects that may be dangerous. 

Cancer warning. Cancer was found in some animals during testing with metronidazole. There may be a similar risk in humans. Metronidazole should only be used to treat conditions approved by the FDA.

Nervous system effects

Metronidazole oral tablets and capsules may cause certain serious conditions that affect the nervous system. These conditions include encephalopathy (abnormal brain function), meningitis (inflammation in the brain), and seizures. They also include peripheral neuropathy (nerve damage in the hands and feet). Call your doctor right away if you have symptoms such as memory loss, trouble focusing, fever, stiff neck, or pain or numbness in your hands or feet.

What is metronidazole?

The metronidazole immediate-release tablet and extended-release tablet are prescription drugs. They’re both taken by mouth. Immediate-release drugs are released into the body right away. Extended-release drugs are released into the body slowly over time.

These tablets are available as the brand-name drugs Flagyl (immediate-release) and Flagyl ER (extended-release). They’re also available as generic drugs. Generic drugs usually cost less. In some cases, they may not be available in every strength or form as the brand-name version. 

Metronidazole tablets may be used as part of a combination therapy. This means you may need to take them with other medications.

Why it's used

Metronidazole immediate-release oral tablets are used to treat a range of infections caused by bacteria or parasites. These include infections that occur in the gastrointestinal tract or reproductive system. 

Metronidazole extended-release oral tablets are used to treat vaginal infections in women.

How it works

Metronidazole belongs to a class of drugs called nitiroimidazole antimicrobials. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions. 

The metronidazole immediate-release and extended-release tablets work by killing bacteria. This relieves the infection.

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metronidazole Side Effects

Oral tablet

More Common Side Effects

The more common side effects that can occur with use of metronidazole include:

  • headache

  • loss of appetite

  • nausea or vomiting

  • diarrhea

  • heartburn

  • cramping in your abdomen (stomach area)

  • constipation

  • metallic taste in the mouth

If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.

Serious Side Effects

Call your doctor right away if you have serious side effects. Call 9-1-1 if your symptoms feel life-threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following:

  • Nervous system effects, including seizures and encephalopathy (abnormal brain function). Symptoms can include:

    • convulsions (sudden movements caused by tightening of your muscles)
    • seizures
    • dizziness
    • headache
    • confusion
    • ataxia (loss of control of body movements)
Pharmacist's Advice
Healthline Pharmacist Editorial Team

Metronidazole doesn’t cause drowsiness.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.
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metronidazole May Interact with Other Medications

Oral tablet

Metronidazole can interact with other medications, vitamins, or herbs you may be taking. An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well.

To help avoid interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbs you’re taking. To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Alcohol interaction

You should stop using drinks that contain alcohol at least 3 days before starting metronidazole. Also avoid alcohol for 3 days after you stop treatment with this drug.

Alcohol can cause side effects when used with metronidazole. These include nausea, vomiting, abdominal cramps, headaches, or flushing (sudden redness and warmth in your face). If you drink alcohol, talk to your doctor about whether this drug is safe for you.

Medications that might interact with this drug

Drugs you should not take with metronidazole

Do not take these drugs with metronidazole. Doing so can cause dangerous effects in the body. Examples of these drugs include: 

  • Disulfiram.
    • Using this drug with metronidazole can cause psychotic reactions. Symptoms can include confusion, hallucinations (seeing or hearing things that aren’t real), or delusions (believing things that aren’t real). Do not take metronidazole if you’ve taken disulfiram during the last 2 weeks.

Interactions that increase your risk of side effects

Increased side effects from metronidazole: Taking metronidazole with certain medications raises your risk of side effects from metronidazole. This is because the amount of metronidazole in your body may be increased. Examples of these drugs include:

  • Lithium.
    • Increased side effects of metronidazole can include a higher risk of QT prolongation (irregular heartbeat).  

Increased side effects from other drugs: Taking metronidazole with certain medications raises your risk of side effects from these drugs. Examples of these drugs include:

  • Warfarin or other blood thinners.
    • Increased side effects of these drugs include a higher risk of bleeding.
  • Busulfan.
    • If possible, you should avoid taking busulfan with metronidazole. If you take these drugs together, your doctor may check the amount of busulfan in your body more often.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we cannot guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.
Metronidazole warnings
liver disease
People with liver disease

Your liver helps process this drug. If you have severe liver disease, your liver may process this drug more slowly. This increases the amount of the drug in your body and raises your risk of side effects. Your doctor may lower your dose of metronidazole, or have you take it less often.

kidney disease
People with kidney disease

Your kidneys help clear this drug from your body. If you have severe kidney disease, your kidneys may process this drug more slowly. This increases the amount of the drug in your body and raises your risk of side effects. Your doctor may lower your dose of metronidazole, or have you take it less often.

Pregnant women
Pregnant women

Metronidazole is a category B pregnancy drug. That means two things:

  1. Studies of the drug in pregnant animals have not shown a risk to the fetus.
  2. There aren’t enough studies done in pregnant women to show if the drug poses a risk to the fetus.

Talk to your doctor if you’re pregnant or planning to become pregnant. Metronidazole should not be taken during the first trimester of pregnancy. For the second and third trimesters, this drug should be used only if the potential benefit justifies the potential risk to the fetus.

breast-feeding
Women who are breast-feeding

Metronidazole may pass into breast milk and cause side effects in a child who is breastfed. 

Talk to your doctor if you breastfeed your child. You may need to decide whether to stop breastfeeding or stop taking this medication.

seniors
For seniors

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This increases your risk of side effects. 

call the doctor
When to call the doctor

Call your doctor right away if:

  • You have completed your treatment with metronidazole and still have symptoms of your infection.
  • You become pregnant while taking this drug.
allergies
Allergies

Metronidazole can cause a severe allergic reaction or hypersensitivity. Symptoms can include:

  • hives (itchy welts)
  • red rash
  • peeling or sloughing of your skin
  • wheezing
  • fever
  • chills 

If you have an allergic reaction, call your doctor or local poison control center right away. If your symptoms are severe, call 9-1-1 or go to the nearest emergency room.

Don’t take this drug again if you’ve ever had an allergic reaction or hypersensitivity to it. In some cases, taking it again could be fatal (cause death).

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How to Take metronidazole (Dosage)

Oral tablet

All possible dosages and drug forms may not be included here. Your dosage, drug form, and how often you take the drug will depend on: 

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

What are you taking this medication for?

Bacterial and amoebic infections

Generic: metronidazole

Form: Oral immediate-release tablet
Strengths: 250 mg, 500 mg

Brand: Flagyl

Form: Oral immediate-release tablet
Strengths: 250 mg, 500 mg
Adult dosage (ages 18–64 years)

Note: Your dosing and length of treatment depend on your infection type.

  • Bacterial infections:
    • Typical dosage: 500 mg, 4 times per day.
    • Maximum dosage: 4 g per day.
  • Amoebic infections (caused by a parasite):
    • Typical dosage: 750 mg, 3 times per day for 5–10 days.
    • Maximum dosage: 4 g per day.
  • Trichomoniasis (a sexually transmitted infection caused by a parasite):
    • Typical dosage: 2 g per day (or 1 g twice per day), or 250 mg, 3 times per day for 7 days.
    • Maximum dosage: 4 g per day.
Child dosage (ages 0–17 years)
  • Amoebic infections:
    • Typical dosage: 35–50 mg/kg per day, given in 3 divided doses for 10 days.
    • Maximum dosage: 2,250 mg per day.
  • Trichomoniasis:
    • Typical dosage: 15 mg/kg per day, given in 3 divided doses for 7 days.
    • Maximum dosage: 1,000 mg per day.
Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This increases your risk of side effects.

Your doctor may start you on a lowered dose or a different medication schedule. This can help keep levels of this drug from building up too much in your body.

Bacterial vaginosis

Brand: Flagyl ER

Form: Oral extended-release tablet
Strengths: 750 mg
Adult dosage (ages 18–64 years)

Note: Your dosing and length of treatment depend on your infection type.

  • Typical dosage: 750 mg per day.
  • Maximum dosage: 4 g per day
Senior dosage (ages 65 years and older)

The kidneys of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, more of a drug stays in your body for a longer time. This increases your risk of side effects.

Your doctor may start you on a lowered dose or a different medication schedule. This can help keep levels of this drug from building up too much in your body.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we cannot guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always to speak with your doctor or pharmacist about dosages that are right for you.
Pharmacist's Advice
Healthline Pharmacist Editorial Team

Metronidazole tablets come with risks if you don’t take them as prescribed.

If you stop taking the drug suddenly or don’t take it at all

Your infection may not improve, and may get worse.

If you miss doses or don’t take the drug on schedule

Your medication may not work as well or may stop working completely. For this drug to work well, a certain amount needs to be in your body at all times.

If you take too much

You could have dangerous levels of the drug in your body. Symptoms of an overdose of this drug can include increased side effects, such as:

  • headache
  • loss of appetite
  • nausea or vomiting
  • diarrhea
  • heartburn
  • cramping in your abdomen (stomach area)
  • constipation
  • metallic taste in your mouth

If you think you’ve taken too much of this drug, call your doctor or local poison control center. If your symptoms are severe, call 9-1-1 or go to the nearest emergency room right away.   

What to do if you miss a dose

Take your dose as soon as you remember. But if you remember just a few hours before your next scheduled dose, take only one dose. Never try to catch up by taking two doses at once. This could result in dangerous side effects.

How to tell if the drug is working

Your symptoms of infection should improve.

Metronidazole is used for short-term treatment.

You can take the immediate-release tablets with or without food

Taking them with food may help to reduce upset stomach.

Do not take the extended-release tablets with food. You should take them at least 1 hour before a meal or 2 hours after a meal.

You can cut or crush the immediate-release tablets

Do not cut or crush the extended-release tablets.

Store this drug carefully

  • Store metronidazole tablets below 86°F (30°C).
  • Keep this drug away from light.
  • Don’t store this medication in moist or damp areas, such as bathrooms.

A prescription for this medication may or may not be refillable

Ask your doctor or pharmacist. You or your pharmacy may have to contact your doctor for a new prescription if you need this medication refilled.

Travel

When traveling with your medication:

  • Always carry your medication with you. When flying, never put it into a checked bag. Keep it in your carry-on bag.
  • Don’t worry about airport x-ray machines. They can’t hurt your medication.
  • You may need to show airport staff the pharmacy label for your medication. Always carry the original prescription-labeled box with you.
  • Don’t put this medication in your car’s glove compartment or leave it in the car. Be sure to avoid doing this when the weather is very hot or very cold.

Are there any alternatives?

There are other drugs available to treat your condition. Some may be better suited for you than others. Talk to your doctor about other drug options that may work for you.

What does the pill look like?

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How Much Does metronidazole Cost?

Oral tablet

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Lowest price for metronidazole

Walmart $9.00
Walgreens $9.66
Duane Reade $9.66
These prices represent the lowest priced national pharmacies for metronidazole on GoodRx. They may be lower than your insurance.

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These prices represent the lowest priced national pharmacies for metronidazole on GoodRx. They may be lower than your insurance.

Show Sources

Content developed in collaboration with University of Illinois-Chicago, Drug Information Group

Medically reviewed by Creighton University, Center for Drug Information and Evidence-Based Practice on January 19, 2016

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.
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