7 Metronidazole Interactions: Alcohol, Lithium, and More

Metronidazole (Flagyl) is a prescription antibiotic that’s used to treat a variety of bacterial and parasitic infections. This includes bacterial vaginosis, sexually transmitted infections (STIs), skin infections, and more. It works by attacking the DNA of bacteria or protozoans (parasites) that are causing your infection.

Metronidazole is an effective and affordable option for treating infections like these, but it has some important interactions to keep in mind. Drug interactions can change the way your medication works in your body or increase your risk of side effects.

Metronidazole interactions list

The best way to handle metronidazole interactions is by having your healthcare team review your medication list. That way, they can identify potential interactions before they become a problem. It also helps to have an idea of common culprits to watch out for. Examples of medications and other substances that can interact with metronidazole include:

• Disulfiram

• Alcohol

• Warfarin (Jantoven)

• Lithium (Lithobid)

• Medications that prolong the QT interval, such as citalopram (Celexa) and levofloxacin

• Cimetidine (Tagamet HB)

• Amiodarone (Pacerone)

• Clarithromycin (Biaxin XL)

• Diltiazem (Cardizem)

• Medications that contain cobicistat (Tybost)

• Phenytoin (Dilantin, Phenytek)

• Phenobarbital

• Rifampin (Rifadin)

• Carbamazepine (Tegretol)

Below, we’ll highlight seven key metronidazole interactions to know about.

1. Disulfiram

Disulfiram is a medication that treats alcohol use disorder. It works by stopping the breakdown of alcohol, making it unpleasant to drink. When you drink an alcoholic beverage while disulfiram is in your system, it causes nausea, vomiting, and other bothersome side effects. This is called a disulfiram-alcohol reaction. It helps discourage people living with alcohol use disorder from consuming alcohol.

If you or a loved one takes disulfiram, it’s also important to use caution if you’re given a prescription for metronidazole. When they’re taken together, the combination can result in psychosis. Psychosis symptoms can include hallucinations, paranoid delusions, and an altered mental state.

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As a result, metronidazole and disulfiram should not be taken together. Metronidazole should be taken only if at least 2 weeks have passed since your last dose of disulfiram.

2. Alcohol

Many people enjoy an alcoholic drink from time to time, but it doesn’t always mix well with medications you may be taking. Metronidazole is no exception.

This interaction is similar to the reaction between disulfiram and alcohol. The interaction between alcohol and metronidazole is called a “disulfiram-like reaction.” You’ll likely experience nausea, vomiting, and/or flushing if you drink alcohol while taking metronidazole.

To avoid having a sour and potentially dangerous evening, avoid alcohol (and alcohol-containing products) while taking metronidazole. You should wait at least 3 days after taking your last metronidazole dose before drinking alcohol.

3. Warfarin

Warfarin is an anticoagulant (blood thinner) medication that prevents and treats blood clots. You may be taking it for several reasons, such as preventing a blood clot after having a heart attack or a stroke.

Sometimes, warfarin’s blood-thinning effects can be too strong. What’s more, many factors can change your warfarin levels, including medications like metronidazole. Metronidazole can enhance warfarin’s effects and cause you to bleed more easily, which can be dangerous.

EXPERT PICKS: WHAT TO READ NEXT

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• Common side effects: Do you feel nauseated after taking metronidazole? Learn about potential metronidazole side effects and tips for managing them.

While you’re taking warfarin, your healthcare team monitors blood tests to reduce your risk of bleeding. But you should also look out for signs of bleeding on your own. Possible symptoms include bleeding that takes a long time to stop, easy bruising, or dark stools. If any of these occur, you should immediately contact your care team.

4. Lithium

Lithium is a first-choice medication for bipolar disorder. Like warfarin, lithium levels are sensitive to small changes. Metronidazole can reduce the kidneys’ ability to clear lithium, causing it to build up in your body. This is especially worrisome if you’re taking a higher dose of lithium.

If you start a prescription for metronidazole, your healthcare team may want to monitor your lithium levels more closely. If your levels become too high, they may adjust your lithium dose out of caution. When lithium levels are too high, you may experience symptoms of lithium toxicity, including:

• Severe confusion or blacking out

• Vomiting that doesn’t stop

• Ringing in the ears (tinnitus) 

• Blurry vision

• Tremors or muscle spasms

• Drowsiness or lightheadedness

• Seizures

If you have symptoms of possible lithium toxicity, contact your care team as soon as possible.

5. Medications that affect your heartbeat

Some medications can prolong the QT interval — the time it takes your heart to reset between heartbeats — which can lead to life-threatening irregular heartbeats. While rare, metronidazole has been linked to QT prolongation. This risk is higher if you take it with other medications that also have this effect, including:

• Citalopram

• Haloperidol (Haldol)

• Methadone (Methadose)

• Levofloxacin

• Ziprasidone (Geodon)

Keep in mind that these aren’t all the medications that prolong the QT interval. Your healthcare team can review your medication list to identify others you may be taking.

6. Cimetidine

If you have heartburn, you may have tried a medication called cimetidine. It helps treat health conditions such as acid reflux (heartburn) and stomach ulcers. But it can cause trouble when taken with metronidazole.

Cimetidine blocks liver enzymes that are responsible for breaking down metronidazole. When taken together, cimetidine can cause levels of metronidazole to go up. This can increase the risk of metronidazole side effects.

Other medications can cause a similar effect. Some examples are: 

• Amiodarone

• Clarithromycin

• Diltiazem

• Medications that contain cobicistat

7. Medications that speed up metronidazole’s clearance

Several medications can speed up your liver’s ability to break down metronidazole. If this happens, it can make metronidazole less effective at treating your infection. Examples of these medications include:

• Phenytoin

• Phenobarbital

• Rifampin

• Carbamazepine

This list is not exhaustive. You should ask a pharmacist to screen for these types of interactions.

Are there any foods or beverages that you need to avoid with metronidazole?

The only food or drink that you need to avoid with metronidazole is alcohol. Others, such as coffee, eggs, bananas, and bread, are safe to have with metronidazole. You can maintain your regular diet. But if metronidazole is making you feel nauseated, it may help to stick with bland foods, such as rice or toast, that are easier on your stomach.

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Written by:

Mandeep Sohal, PharmD

Mandeep Sohal, PharmD, is a licensed pharmacist in California with over 7 years of experience. In his career, he’s worked in specialty and community pharmacy, pharmacy benefit management, and pharmaceutical manufacturers.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

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