11 Foods Not to Mix With Prescription Medications

Some foods and drugs don’t mix.

When taking prescription medications to lower your cholesterol, prevent blood clots, treat an infection or ease depression, you may need to avoid foods or beverages that cancel out — or overly heighten — the desired drug effect. Certain foods can interact with more than one type of drug.

In some cases, you can tweak meal timing around scheduled doses to keep enjoying favorite foods. Here are some common food-drug interactions and how to prevent them:

Green leafy vegetables

Spinach, kale, collard greens and broccoli are super-healthy but they can make medications to prevent blood clots less effective. Green leafy veggies are rich in vitamin K, which interacts with the common blood-thinning drug warfarin (Coumadin). Vitamin K is used by the body to make some blood-clotting factors, whereas warfarin reduces the action of vitamin K. .

Tasha Woodall, associate director of pharmacotherapy in geriatrics with the Mountain Area Health Education Center in Asheville, North Carolina, often talks about workarounds for patients on drugs like warfarin. “I tell people frequently: You really don’t need to avoid eating green leafy vegetables. They’re good for you, certainly. But the key is to be consistent.”

Patients taking warfarin regularly have their blood levels monitored. “I’ve certainly taken care of people on warfarin who’ve been stable for a long time and they eat spinach, kale, collard greens, every meal of the day,” says Woodall, who is also an associate professor of clinical education at UNC Eshelman School of Pharmacy. “The problem comes when somebody eats a spinach salad every day for a few weeks until the bag of spinach runs out, and then goes the next week without eating any.” Instead, predictable consumption allows medication to be adjusted accordingly.


Mayonnaise — and certain oils such as canola, soybean and olive oils — also change how warfarin works in your body. Mixing green veggies with mayo results in a vitamin K double whammy.

“People who are having a lot of coleslaw: They’ve got the cabbage, which has vitamin K, mixed in with some mayonnaise,” Woodall notes.


Grapefruit can impact how digestive enzymes break down and how the body absorbs a number of medications.

“If somebody likes to eat grapefruit or drink grapefruit juice, there are certain substances that may affect the way the body handles the medication,” says Mandy Leonard, senior director of pharmacy at Cleveland Clinic. “This can potentially result in fluctuating levels of that medication in the body.”

Grapefruit can interact with these drugs or drug classes:

— Statin drugs to manage cholesterol including Lipitor (atorvastatin), Zocor (simvastatin) and Mevacor (lovastatin).

— Erectile dysfunction drugs like Viagra (sildenafil).

— Chemotherapies such as vincristine and docetaxel.

— Calcium channel blockers to treat high blood pressure.

— Immune-suppressing drugs like cyclosporine for transplant patients.

— Allergy medications with fexofenadine like Allegra.

It’s more likely that drinking grapefruit juice in large quantities, rather than eating a single grapefruit in the morning, would cause systemic side effects. “My sense is we would have to be talking about somebody who primarily drinks grapefruit juice, as opposed to other liquids,” Woodall says.


Alcohol is a beverage that can interact with a wide variety of drugs. “One of the questions I get a lot as a pharmacist is: I was just placed on this medication — can I drink alcohol?” Leonard says. “There are some medications for which you have to absolutely avoid alcohol because there are really bad reactions to it. But, in general, I normally say, ‘You just have to be careful.'”

Alcohol can affect antibiotics and other drugs including:

Metronidazole (Flagyl). This antibiotic is “definitely one where people should not drink any alcohol,” Leonard says. Patients taking Flagyl are even told to avoid alcohol-containing mouthwashes.

Warfarin (Coumadin). “If someone has several beers in one evening, then their liver enzymes are so busy trying to process the alcohol that they’re not necessarily processing the warfarin,” Woodall says. “Therefore you end up with higher levels of warfarin and higher levels of blood thinning.”

Diabetes drugs. With insulin and oral diabetes drugs, alcohol can extend their effects and result in too-low blood sugar.

Antihistamines. Taking sedating drugs like Benadryl with alcohol increases side effects like drowsiness.

Acetaminophen pain relievers. Prescription drugs containing acetaminophen should not be taken with alcohol because of possible liver damage. “Some individuals appear to be more susceptible to acetaminophen-induced liver toxicity than others,” according to the Food and Drug Administration. “People who use alcohol regularly may be at increased risk for toxicity, particularly if they use more than the recommended dose.”

Antidepressants. Alcohol may ease your mood at first, but it eventually acts as a depressant on the central nervous system. If you take antidepressants, talk to your doctor about alcohol.

Meat and fish

High-protein foods such as meat or fish can compete with dopamine drugs. “Dopamine is the neurotransmitter that’s deficient in the brains of people with Parkinson’s disease,” Woodall explains. “The most effective treatment we have for them is to more or less replace dopamine with a medication like Sinemet.” Levodopa, which converts to dopamine in the brain, is the active ingredient in Sinemet.

Dopamine, however, is an amino acid, or a protein building block. “We tell people to try to avoid taking Sinemet with a really protein-rich food — don’t take it with a steak,” Woodall says. Otherwise, “you’re experiencing an onslaught of amino acids in the gastrointestinal tract.” Between the high-protein food and the levodopa drug, “there’s going to be some competition to be absorbed,” she says. Therefore, Parkinson’s symptoms may not be as well-controlled.

To avoid this interaction, your doctor may suggest taking the medication on an empty stomach or that you save higher protein amounts for the end of the day, notes the website of the Michael J. Fox Foundation for Parkinson’s Research.


Dairy products can interact with medications. Components of milk and dairy food, like the protein casein and minerals such as calcium and magnesium, can interfere with drug absorption in the body.

— Antibiotics can be affected by consuming milk, yogurt or cheese around the time of taking the drug.

— Thyroid drugs don’t always mix well with dairy. “Calcium, whether that’s a calcium supplement pill you’re swallowing or the calcium in dairy foods, can interfere with absorption of things like thyroid-replacement medications,” Woodall says.

Chocolate, pickled, cured and fermented foods

Aged cheeses, smoked fish, chocolate, beer, wine and some processed meats all contain tyramine, a substance that interacts with specific drugs to treat depression. With this older class of antidepressants, called monoamine oxidase inhibitors, tyramine slows their breakdown in the body. This can lead to a hazardous rise in blood pressure.

“Before patients are put on these medications, there’s a lot of education that goes on,” Leonard says. Pharmacists and dietitians work with patients so they know how to avoid foods high in tyramine.

Potassium-rich foods

Avocados, potatoes, spinach, white beans and bananas are all good sources of potassium, an important mineral for regulating your heartbeat and maintaining fluid balance in the body, among other functions. However, potassium-rich foods may interact with certain blood pressure medications that can lead to high potassium levels and the potential for abnormal heart rhythms.

Doctors routinely check potassium levels for patients on drug classes including angiotensin-converting enzyme inhibitors, angiotensin II receptor blockers and potassium-sparing diuretics.

It’s challenging for consumers to keep track of every potential food-drug interaction. “Most of the more concerning ones are actually going to be on the bottle,” Leonard points out. Stickers highlight important food-drug interactions and instructions like taking a drug on an empty stomach or avoiding alcohol.

St. John’s wort

St. John’s wort, although touted as an herbal remedy, can actually reduce the effect of evidence-based treatments. “St. John’s wort is notorious — it has so many different interactions,” Woodall says. By causing the liver to release certain enzymes, St. John’s wort in herbal teas or supplements can interfere with medications including:

— Statin drugs to treat high cholesterol.

— The ED drug Viagra.

— Digoxin medications for heart conditions.


Drinking large quantities of coffee or energy drinks could exacerbate the effects of drugs that stimulate the central nervous system. “A lot of people ask about caffeine,” Leonard says. “Caffeine is a stimulant. If somebody’s on a stimulant and they take caffeine, they could increase (the effect).”

Peanut-containing drugs

If you have a peanut allergy, in addition to peanuts in foods, certain medications potentially pose a problem. “There are some drugs that contain some peanut components,” Leonard says. Prometrium capsules, a type of hormone drug, contains peanut oil. For any patient with a severe peanut allergy, she says, “We will look at their medications or ones that they want to be started on just to make sure there’s no kind of component with peanut in it.”

Ask about interactions.

When starting a new prescription medication, talk to your doctor, pharmacist or dietitian about potential food-drug interactions. When you need information, don’t be put off by the line of customers at the pharmacy counter.

“It’s just the right of the patient to be provided counseling by a pharmacist,” Leonard says. “And even if it’s a quick, ‘Yes, I would like to speak to the pharmacist for a minute or two.’ You, as the patient, have the right to that, (although) a lot of people don’t take advantage of it,” she says. “But that’s what we’re there for.”

Food-drug interactions

These foods, beverages or nutrients may alter the impact of specific prescription medications:

— Foods high in vitamin K, like green leafy vegetables.

— Mayonnaise and cooking oils.

— Grapefruit.

— Alcohol.

— High-protein foods, like meat and fish.

— Dairy/calcium.

— Tyramine-rich foods, such as chocolate, pickled, cured and fermented foods.

— Potassium-rich foods, such as avocados, potatoes, spinach, white beans and bananas.

— St. John’s wort.

— Caffeine.

— Peanut components in drugs.

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11 Foods Not to Mix With Prescription Medications originally appeared on usnews.com

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