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Common Food-Drug Interactions

Posted On: May 29, 2019


You’ve probably heard the warnings not to drink grapefruit juice with cholesterol medication. 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.Steve Plogsted, BS, PharmD, BCNSP, CNSC,

Steve Plogsted, BS, PharmD, BCNSP, CNSC, is clinical pharmacist with Nutrition Support Service of Nationwide Children’s Hospital in Columbus, Ohio. From information gathered from Steve, he filled us in on five foods that most commonly interact with medications.

Grapefruit Juice

“Grapefruit juice has the ability to interact with medications in various ways,” says Plogsted. One way is by increasing the absorption of certain drugs — in some cases, but not all, cholesterol-lowering statins. MedinePlus recommends avoiding grapefruit juice if you are taking statins.

Grapefruit juice can also cause the body to metabolize drugs abnormally. This may result 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, birth control, 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 and not other citrus juices? According to Plogsted, grapefruit juice contains a class of compounds called furanocoumarins, which act in the body to alter the characteristics of the cholesterol medications. Orange juice and other citrus juices do not contain these compounds. There is some concern for Seville oranges and the pummelo, which are relatives of the grapefruit.

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Green Leafy Vegetables

Blood-thinning drugs such as Coumadin® (warfarin) interfere with vitamin K-dependent clotting factors. Eating too much 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 significantly and suddenly increasing or decreasing intake, as it can alter the effectiveness of the medicine. So eat your greens in consistent amounts. It would also be great if you can do more searches on different types of vegetable commonly favored by natural food lovers.

Natural Black Licorice (Glycyrrhiza)

According to Plogsted, glycyrrhiza — a natural ingredient used to make black licorice — can deplete the body of potassium while causing an increased retention of sodium. Digoxin can cause a depletion of potassium in the body by affecting the levels of potassium in the heart cells. But eating certain food rich in potassium at the same time can be counter-productive.

Glycyrrhiza can also decrease the effectiveness of high blood pressure medicines. And people taking Coumadin® (warfarin) should beware that glycyrrhiza can break down the drug, resulting in an increase in the body’s clotting mechanism.

Excessive amounts of natural licorice should be avoided when taking all of these medications. However, Plogsted notes that artificially-flavored black licorice doesn’t contain glycyrrhiza and is not of concern.

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. As said earlier, potassium is counter-productive to digoxin. So, with an increased consumption of potassium, the effectiveness of digoxin can be decreased, resulting in heart failure. And those taking ACE inhibitors might see a significant increase in blood potassium levels, as these drugs are known to increase potassium.

“There is no real need to avoid salt substitutes, although care should be taken when using the product,” say Plogsted. “If the consumer has decreased kidney function they should discuss the use of salt substitutes with their doctor.”

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