Food and Drug Interactions

By Charlyn Fargo

January 18, 2019 7 min read

You've probably heard the warnings not to drink grapefruit juice with blood thinners. However, that isn't the only combination of food and drugs to avoid. Grapefruit juice can interact with numerous other medications, both prescription and over-the-counter. And many other foods commonly interact with drugs, too.

Here are four foods that most commonly interact with medications, according to the Academy of Nutrition and Dietetics.

1. Grapefruit Juice

One way grapefruit juice interacts with medication is by increasing the absorption of certain drugs — as is the case with some, but not all, cholesterol-lowering statins. MedlinePlus recommends avoiding grapefruit juice if you are taking statins. Grapefruit juice also can cause the body to metabolize drugs abnormally, resulting in lower- or higher-than-normal blood levels of the drug. Many medications are affected in this way, including antihistamines, blood pressure drugs, thyroid replacement drugs, oral contraceptives, stomach acid-blocking drugs and the cough suppressant dextromethorphan. It's best to avoid or significantly reduce intake of grapefruit juice when taking these medications. But why is grapefruit juice of concern but not other citrus juices? Grapefruit juice contains a class of compounds called furanocoumarins, which act in the body to alter the characteristics of these medications. Orange juice and other citrus juices do not contain these compounds.

2. Green Leafy Vegetables

Blood-thinning drugs such as Coumadin (warfarin) interfere with vitamin K-dependent clotting factors. Eating too many green leafy vegetables, which are high in vitamin K, can decrease the ability of blood-thinners to prevent clotting. But you don't have to give up greens altogether. Problems arise from increasing or decreasing intake significantly and suddenly, as this can alter the effectiveness of the medicine. So eat your greens in consistent amounts rather than avoid them altogether.

3. Natural Black Licorice (Glycyrrhiza)

This natural ingredient used to make black licorice can deplete the body of potassium while causing an increased retention of sodium. When the body is depleted of potassium, the activity of digoxin, a medication used to treat heart failure, can be greatly enhanced, resulting in the heart not beating properly. Glycyrrhiza also can decrease the effectiveness of high blood pressure medicines. And people taking Coumadin (warfarin) should beware that glycyrrhiza can break down the drug, increasing the body's clotting mechanism. Excessive amounts of natural licorice should be avoided when taking any of these medications. However, artificially flavored black licorice doesn't contain glycyrrhiza and is not of concern.

4. Salt Substitutes

Consumers taking digoxin for heart failure or ACE inhibitors for high blood pressure should be careful with salt substitutes, which, most often, replace sodium with potassium. An increased consumption of potassium, can decrease the effectiveness of digoxin, resulting in heart failure. And those taking ACE inhibitors might see a significant increase in blood potassium levels, as these drugs are known to cause.

The bottom line? When receiving a prescription for a new medication or taking a new over-the-counter drug, always read drug warning labels and ask your physician or pharmacist about which foods or other drugs you should avoid or be concerned about taking.

Q and A

Q: Should I drink water during meals?

A: There has been some confusion about the importance of drinking water with meals and snacks. In fact, there have even been some concerns regarding water intake and negative impacts on digestion. However, Michael Picco, a physician from the Mayo Clinic, notes: "There's no concern that water will dilute digestive juices or interfere with digestion. In fact, drinking water during or after a meal actually aids digestion." Regular and adequate water intake is essential for good health. Especially important is to consume enough water (and other beverages) to ensure that your body is able to effectively absorb and use the nutrients in the food you eat. An added bonus? Water acts as a natural stool softener and helps to prevent or lessen constipation. Drinking a glass of water around mealtime can also help take the edge off of hunger and may assist in weight management. It's always important to consider your own personal situation: If you have been advised by a physician to limit water or fluids at any point throughout the day, heed that advice. If you want to increase water intake, be sure to bring it up at your next medical appointment.

Information courtesy of Environmental Nutrition.


Cauliflower seems to be in everything these days, as it's a way to reduce carbohydrates. Here's a recipe for cauliflower English muffins from Eating Well magazine that uses riced cauliflower in place of flour.


5 cups cauliflower florets (about 1 pound)

1 cup shredded sharp cheddar cheese

1 large egg, lightly beaten

1/8 teaspoon salt

Preheat oven to 425 F. Line a large baking sheet with parchment paper. Place cauliflower in a food processor. Process until finely grated. Transfer to a microwave-safe bowl. Cover loosely and microwave on high for 3 minutes. Let cool slightly. Transfer the cauliflower to a clean kitchen towel and wring out excess moisture. Return to the bowl and stir in cheddar, egg and salt until thoroughly combined. Place a 3-inch biscuit cutter on the prepared baking sheet. Fill the cutter with about 1/4 cup of the batter, patting it down slightly in the mold. Repeat with the remaining batter, leaving about 1 inch between each one, until you have 8 "muffins." Bake until browned and crispy around the edges, about 25 minutes. Serve with your favorite toppings or use to make a breakfast sandwich. Makes 8 muffins.

Per serving (2 muffins): 165 calories, 11 grams protein, 8 grams carbohydrates, 11 grams fat (6 grams saturated fat), 74 milligrams cholesterol, 3 grams fiber, 315 milligrams sodium.

Charlyn Fargo is a registered dietitian at Hy-Vee in Springfield, Illinois, and the media representative for the Illinois Academy of Nutrition and Dietetics. For comments or questions, contact her at [email protected] or follow her on Twitter @NutritionRD. To find out more about Charlyn Fargo and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at

Photo credit: at Pixabay

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