7 Metronidazole Interactions: Does any Interaction Mean Contraindication?

Common Metronidazole Drug Interactions

Metronidazole is an antibiotic that is usually prescribed for certain intestinal and gynecological infections. This medication is effective for treating diseases caused by bacteria and microscopic parasites of the reproductive system, gastrointestinal tract, and other body areas (1-3).

While metronidazole is quite effective for the treatment of infections, using it in combination with certain drugs might cause adverse reactions; some are serious enough that these medications should not be used together (1-2).

To avoid potentially harmful adverse effects, patients should be aware of the following drugs that interact with metronidazole.

1. Disulfiram

Disulfiram is a medication used for the treatment of chronic alcoholism. Disulfiram works by interacting with alcohol and causing drinking to be unpleasant due to nausea, vomiting, abdominal cramps, and headache, thus discouraging consumption (4). If a patient uses disulfiram and takes metronidazole, the patient may develop confusion, hallucinations, and inappropriate behavior (1, 2, 4, 5).

Therefore, metronidazole is not recommended for patients who take disulfiram, including a week after taking the last disulfiram dose. (1-2)

Symptoms of Disulfiram-like Reactions

Symptoms of Disulfiram-like Reactions

2. Alcohol

In some patients, drinking alcohol while taking oral metronidazole can cause nausea, vomiting, abdominal cramps, and headache. This is similar to the effect of disulfiram, a medication that is used to treat alcohol abuse (1-2) and is called “disulfiram-like reaction.”

While this may not be applicable to many patients, all patients are advised to avoid alcohol consumption while taking metronidazole, and for at least three days after the end of therapy (1-2).

3. Warfarin

Warfarin is an anticoagulant that prevents blood clots from forming or growing bigger in the blood vessels, and is used to treat various conditions that predispose patients to forming blood clots.  If given in excess amounts, it can cause spontaneous bleeding and bruising.

Metronidazole inhibits the breakdown of warfarin in the body, thus causing excess and may cause life-threatening bleeding (9-11). Therefore, either close monitoring, changing antibiotic, or changing anticoagulant might be appropriate, depending on the physician’s recommendation.

4. Lithium

Lithium is the first mood stabilizer developed and is still one of the most popular medications used for bipolar disorder treatment. It is a long-term therapy, and many patients depend on lithium to achieve disorder stability.

Metronidazole can slow down the body’s clearing out of lithium and increase its levels, which can cause toxic effects (1, 2, 14).  Therefore, it is critical that the doctor who prescribes metronidazole is aware of lithium prescription to prevent harmful adverse effects.

5. Busulfan

Busulfan is a medication used to treat leukemia and other types of blood cancers. This medication inhibits the growth of cancerous cells (15).

Metronidazole, when used with busulfan, can increase busulfan concentrations in the blood, which increases the risk for busulfan toxicity.

Due to the busulfan toxicity risk, metronidazole is not recommended to patients using busulfan unless the doctor decides that the benefit of metronidazole treatment is more beneficial than the possible risk. In such cases, the doctor will monitor busulfan plasma concentration and adjust the dose accordingly. (1-2)

6. Phenytoin

Phenytoin is a medication commonly used to treat seizure disorder. When patients taking phenytoin start taking metronidazole, the blood levels of phenytoin can increase, resulting in toxic effects, such as abnormal eye movements, slurred speech, and confusion. Additionally, metronidazole levels may decrease as a result of phenytoin intake, resulting in reduced effectiveness of the drug. For these reasons, it is important for all physicians involved in the care of the patient to be aware of medications prescribed by other physicians (25).

7. Drugs That Can Cause Heart Arrhythmias

Metronidazole, in combination with certain medications, can increase the risk of developing irregular heartbeat (also called arrhythmia). This could be very serious and even fatal, so it is important to be aware of this risk when combining metronidazole with certain psychiatric drugs (including citalopram, amitriptyline, and quetiapine), some heart medications (including amiodarone, sotalol, and flecainide), and a few other various prescriptions (including methadone, sumatriptan, and ondansetron). Therefore, it is imperative for the patient to inform the physician of the medications that have been prescribed (1, 2, 24).


As with any other medication, metronidazole can interact with certain other drugs and develop adverse effects. Patients should avoid drinking alcohol and inform the doctor and the pharmacist of all the drugs that they are taking or have taken in the past week before starting metronidazole.

In addition, patients should read the medication guide carefully and learn about possible side effects of metronidazole to keep the treatment safe and effective.

Metronidazole Interactions FAQ

Can I drink alcohol while taking metronidazole?

No, it is not recommended to drink alcohol while taking metronidazole. Combining alcohol with metronidazole may cause a severe reaction called the “disulfiram reaction,” which produces symptoms such as flushing, headache, nausea, vomiting, and rapid heartbeat.

Can metronidazole interact with other medications?

Yes, metronidazole can interact with other medications, including blood thinners, lithium, and certain seizure medications. It is essential to inform your doctor or pharmacist of all medications you are taking before starting metronidazole.

Can metronidazole interact with herbal supplements?

Yes, metronidazole can interact with herbal supplements, including St. John's wort and garlic supplements. These interactions can lead to an increased risk of side effects or decreased effectiveness of the medication.

Can metronidazole interact with birth control pills?

Yes, metronidazole can interact with birth control pills. It is recommended to use an additional form of contraception, such as condoms, while taking metronidazole and for at least 48 hours after finishing the medication.

Can metronidazole interact with food?

Yes, metronidazole interacts with some foods, especially those containing propylene glycol. It can be found in drink mixes, bread and dairy products, cake mix, dressings, dried soups, frosting, liquid sweeteners, and soft drinks. It may cause an adverse reaction when taken with metronidazole.

See Also

Tramadol Contraindications

Tramadol Side Effects

Tramadol Interactions

Gabapentin Interactions

Shingles Vaccine Side Effects

Lisinopril Contraindications

Is Ibuprofen a Blood Thinner?

Do Blood Thinners Affect Oxygen Levels?

What is Creatinine Level in Blood Tests?

Acetaminophen Contraindications

Aspirin Contraindications

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