What to avoid while taking metronidazole

Metronidazole (brand name Flagyl) is a nitroimidazole antibiotic that is most commonly used to treat vaginal infections, certain sexually transmitted diseases (STDs), and gastrointestinal infections such as H. pylori. It can also treat parasitic infections, like giardia, and is frequently used off-label (for a non-FDA-approved use) to help treat Crohn’s disease, bite wounds, and oral infections. In other words, there are many different reasons you might be prescribed this medication—either orally or topically. While taking this medication, there are certain things you should avoid eating and drinking, such as alcohol and any foods containing propylene glycol. Both substances increase your risk for side effects while taking metronidazole.

How metronidazole works

Metronidazole was originally created to treat parasitic infections but was eventually found to be a powerful antibacterial medication. It is toxic to the organisms that cause certain parasitic and bacterial infections, stopping them from growing and spreading.

Oral metronidazole—prescribed for ailments such as bacterial vaginosis, trichomoniasis, and stomach infections—begins working within a few hours, with most treatment courses lasting between seven and fourteen days. Topical use of metronidazole for skin conditions like rosacea takes longer to work; dermatologists often recommend using it two times a day for a few months.

Foods to avoid with metronidazole

Many antibiotics include a warning to avoid certain foods and beverages because they can interfere with how well the drug is absorbed or increase the antibiotic’s side effects. The same is true for metronidazole. Two things can increase your risk for unwanted side effects like nausea, vomiting, and dizziness: alcohol and propylene glycol, according to Lily Grobman, PA, a certified physician assistant with Medical Offices of Manhattan.

1. Alcohol

Alcohol is firmly off-limits for the entire course of treatment with metronidazole—and for about 3 days after your last dose. Mixing the two can cause the following side effects:

• Nausea, vomiting, and stomach cramps, which can be severe
• Fast heartbeat
• Headache
• Flushing

2. Propylene glycol

Propylene glycol is a common food additive, and mixing this additive with metronidazole can result in the same side effects as alcohol. Propylene glycol can be found in various packaged and processed foods, such as: 

• Baked goods
• Desserts
• Prepared meals
• Baking mixes
• Flavoring mixes
• Candy 
• Popcorn
• Fast food products
• Soft drinks
• Certain breads
• Bacon 
• Canned beans
• Dairy 
• Condiments 
• Food flavoring and coloring

What’s more, Grobman says you should avoid alcohol and any food or drink containing propylene glycol for three days after stopping metronidazole since some of the drug will remain in your system after your last dose. Be sure to check food labels carefully for either of these ingredients.

What should you eat while taking metronidazole?

Metronidazole can be taken with or without food unless you’re prescribed the extended-release tablets, which should be taken on an empty stomach—one hour before or two hours after eating. Taking metronidazole with a bland food (like crackers) can reduce gastrointestinal side effects, suggests Inna Melamed, Pharm.D., functional medicine practitioner and author of Digestive Reset.

Some people choose to eat probiotic-rich foods or take a probiotic supplement while taking antibiotics to help reduce stomach problems. Additionally, in the case of bacterial vaginosis, this may improve your outcome, per a 2020 study.

Other things to avoid with metronidazole

In addition to avoiding alcohol and some other foods with metronidazole, there are several drug interactions. One of the most notable is disulfiram, a medication used to treat alcohol dependence; you shouldn’t take metronidazole if you’ve used disulfiram in the last two weeks.

Before taking metronidazole, tell your healthcare provider about all medications you are taking, including prescription and over-the-counter (OTC) drugs, vitamins, and supplements. Metronidazole may also interact with the following medications:

• Warfarin, a blood thinner
• Lithium, a mood-stabilizing medication
• Phenytoin or phenobarbital, epilepsy medications
• Busulfan
• Mycophenolate
• Cimetidine

Grobman notes that many over-the-counter (OTC) cold and cough syrups also contain propylene glycol, so check ingredient labels carefully before choosing one from the pharmacy or supermarket.

There are no specific warnings against taking metronidazole with other common OTC drugs, like Tylenol or NSAID pain relievers, and daily vitamins or supplements. That said, this isn’t a comprehensive list of medications and supplements to avoid with metronidazole. Always check with a pharmacist or provider who knows your medical history and current medications.

Individuals with Cockayne syndrome should avoid metronidazole because it can cause life-threatening liver failure. Patients with medical conditions such as kidney disease, liver disease, peripheral neuropathy, or an active yeast infection should seek medical advice from a healthcare provider before taking metronidazole.

Finally, some experts suggest metronidazole should be avoided in the first three months of pregnancy. Still, other studies haven’t shown any evidence of a risk to the mother or baby with metronidazole use during pregnancy. If you’re pregnant, trying to become pregnant, or breastfeeding, talk to a healthcare professional so they can help you weigh the pros and cons of using metronidazole.

Gastrointestinal side effects of metronidazole

Antibiotics are often associated with gastrointestinal side effects because they disrupt the typical bacterial environment in the stomach, a.k.a. your gut flora. Many people experience digestive issues like nausea, diarrhea, stomach pain or cramping, constipation, and loss of appetite when taking antibiotics. In addition to headaches and a bitter or metallic taste in the mouth, these are the most common side effects of metronidazole.

As Dr. Melamed explained, eating bland foods with your antibiotics can reduce some of the digestive side effects, but be cautious with the foods on this list—taking your prescription with the foods that interact with metronidazole can affect how well the medication works for you.

While you may experience some mild stomach upset while taking metronidazole, any persistent diarrhea, cramping, vomiting, or fever should be reported to your healthcare provider as soon as possible. If you have any dizziness, slurred speech, numbness, stiff neck, or loss of muscle coordination, you should seek emergency medical attention.