Flagyl (Metronidazole): Uses, Side Effects, and More

An antibiotic prescribed for infections and some conditions

Flagyl (metronidazole) is a broad-spectrum antibiotic. It is used to treat certain bacterial infections and some parasitic infections. At times, it may also be used to treat complications of inflammatory bowel disease (IBD).

Available in cream, syrup, and tablet form, this drug can be very effective. But there are some metronidazole side effects that you should be aware of, including diarrhea, vomiting, and dry mouth. Side effects of metronidazole can range from mild to severe.

Common Side Effects of Flagyl (Metronidazole)
 Verywell / Gary Ferster

This article discusses Flagyl (metronidazole) and how it's used to treat infections. It also talks about its various side effects and other important information you need to know.

What Metronidazole Is Used For

Flagyl syrup or tablets are used to treat or prevent a wide variety of bacterial infections, as well as some conditions. These include those in the abdomen, bones, joints, nervous system, respiratory tract, intestines, and skin.

Flagyl may also be used to treat sexually transmitted infections (STIs), as well as bacterial vaginosis, a condition that causes a bacterial imbalance in the vagina.

Metronidazole cream may be used to treat rosacea, a skin condition that causes face reddening and red bumps that may look like acne.

Is Flagyl Used For UTIs?

Using Flagyl for a urinary tract infection (UTI) is not common, as other drugs are considered better options.

Treatment of IBD Diarrhea

In some cases, Flagyl may be used to treat infections or other complications of IBD. It might be given alternately or at the same time as ciprofloxacin, another type of antibiotic.

Antibiotics kill off bacteria in the body. But many can't distinguish between different bacteria types. Therefore, with some antibiotics, "good" bacteria in the colon may be killed along with the "bad." This results in diarrhea.

However, Flagyl doesn't tend to cause antibiotic-associated diarrhea. In fact, it may be a treatment for it.

Metronidazole Side Effects

Metronidazole side effects range from mild to severe. Common side effects include:

Other possible side effects include:

Though rarer, the more serious side effects of Flagyl include:

If you experience serious side effects, immediately call your healthcare provider or seek medical care.

How Safe Is Metronidazole?

Besides having the potential to cause mild to severe side effects, Flagyl also has a black box warning as it has caused cancer in animal studies.

Precautions and Contraindications

People with an allergy or sensitivity to metronidazole should not take Flagyl. Anyone with liver disease should be closely monitored by their healthcare provider if they take this medication. Yeast infections may get worse while taking Flagyl.

Individuals should avoid taking Flagyl during the first trimester of pregnancy. According to the Food and Drug Administration (FDA), the effect that Flagyl has on an unborn child has not been studied extensively. Flagyl should only be used during pregnancy if it is clearly needed.

Tell your prescribing healthcare provider if you become pregnant while you are taking Flagyl. Flagyl passes into breast milk and could affect a nursing infant. It should be used with caution in people who are breastfeeding.

Dosage and How to Take Flagyl

When taken at home to treat an infection, Flagyl is taken orally in tablet or syrup form. Dosage for adults typically ranges from 250 to 750 milligrams (mg) two to three times per day, often for five or more days. However, dosage will vary depending on the condition being treated.

In order for metronidazole to effectively kill harmful bacteria, it is important to maintain a consistent level of the drug in the blood. Therefore, it must be taken at regular intervals without missing any doses.

Take Flagyl with 8 ounces of water. Flagyl can be taken by itself, or it can be taken with meals. If dry mouth becomes a problem, try chewing gum. You can also suck on hard candy or ice chips.

How Long Does It Take Metronidazole to Work?

Flagyl works quickly. Once taken, Flagyl is quickly absorbed and gets into the bloodstream within a couple of hours. For certain conditions only one day of treatment may be prescribed.

If You Miss a Dose

When you miss a dose, take it as soon as you remember. If you need to take the next dose soon, skip the missed dose and only take the next scheduled dose. Don't double up or take more than one dose of Flagyl at a time.

Stopping Flagyl

Do not stop Flagyl before taking all the doses. After a few days of treatment, most people start to feel better. But that doesn't mean the infection is entirely gone. Take all of the medication that was prescribed unless your healthcare provider tells you to stop taking it.

Stopping the medication before the bacterial infection is completely gone can cause serious consequences. A stronger strain of bacteria may develop. The infection may come back again and be more difficult to treat.

Interactions

Flagyl could interact with several drugs. Tell the prescribing healthcare provider about all drugs and nutritional supplements you are taking.

You should especially mention these from the following list, which may interact with Flagyl:

  • Alcohol
  • Amprenavir
  • Anticoagulants (such as warfarin)
  • Antabuse (disulfiram)
  • Barbiturate medicines for inducing sleep or treating seizures (convulsions)
  • Carbamazepine
  • Cimetidine
  • Dofetilide
  • Fluorouracil
  • Lithium
  • Methadone
  • Phenytoin
  • Sirolimus
  • Tacrolimus

Alcohol

You should not drink alcoholic beverages until 72 hours (three days) after you take the last dose of Flagyl. Drinking alcohol while taking Flagyl could result in abdominal cramps, nausea, vomiting, headaches, and flushing.

Flagyl can also change the taste of alcohol. Take care to avoid alcohol from unexpected sources, such as over-the-counter cough suppressants or cold medications (NyQuil, for example).

Milk Thistle

Milk thistle (Silybum marianum) may help to protect the liver from medications that may harm it, such as Flagyl. It has not been studied in relation to Flagyl, but it may be prescribed as a complementary therapy.

Summary

Flagyl, also known as metronidazole or by the brand name Protostat, is an anti-bacterial drug that treats anaerobic bacterial infections or protozoal infections. It's important to follow your provider's instructions when you take this medication.

Metronidazole side effects may include abdominal cramping, diarrhea, nausea, vomiting, loss of appetite, and headache. Some individuals experience more serious side effects such as numbness or seizures. If you experience severe side effects, call your healthcare provider right away.

Frequently Asked Questions

  • How can I reduce the side effects of metronidazole?

    To help reduce side effects, make sure you take Flagyl exactly as prescribed. Take it after a meal or snack to help with nausea. Drink plenty of water to avoid dehydration, which can make certain side effects worse.

  • Can Flagyl be used for a yeast infection?

    Flagyl should never be used to treat a yeast infection. In fact, using it might worsen the effects of a yeast infection.

  • How long should I wait to drink alcohol after using Flagyl?

    After the last dose of Flagyl is taken, wait at least three days before drinking any alcohol.

  • Is metronidazole available over the counter?

    No, metronidazole is not available over the counter. You will need to contact your healthcare provider to receive a prescription.

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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.