Green leafy vegetables, which are high in vitamin K, can decrease the ability of blood-thinners to prevent clotting. Blood-thinning drugs such as Coumadin® (warfarin) interfere with vitamin K-dependent clotting factors. It is not necessary to avoid greens altogether, but problems arise from significantly and suddenly increasing or decreasing intake, as it can alter the effectiveness of the medicine.
Grapefruit juice increases the absorption of several drugs, for example cholesterol-lowering statins, so it is recommended to avoid grapefruit when taking statins. Unlike other citrus juices, grapefruit contains furanocoumarins, a class of compounds that alter characteristics of medications. Thus, grapefruit juice 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.
Glycyrrhiza, a natural ingredient used to make black licorice, can deplete the body’s potassium while causing an increased retention of sodium. With potassium depletion, the activity of the heart failure medication digoxin, can be greatly enhanced, resulting in an abnormal heartbeat. Glycyrrhiza also can decrease the effectiveness of high blood pressure medicines and can break down warfarin, causing an increase in the body’s clotting mechanism. Excessive amounts of natural licorice should be avoided when taking all of these medications. However, artificially-flavored black licorice is not a concern because it doesn’t contain glycyrrhiza.
Salt substitutes typically replace sodium with potassium, and the increased intake of potassium can reduce the effectiveness of digoxin, resulting in heart failure. Additionally, ACE inhibitors might cause a significant increase in blood potassium levels, as these drugs are known to increase potassium.
Tyramine is an amino acid found in chocolate, aged cheese, smoked meats, fermented soy, and draft beers. Several medications interfere with the breakdown of tyramine, including monoamine oxidase inhibitors used to treat depression and drugs used to treat the symptoms of Parkinson’s disease.
Always read drug warning labels and ask your physician or pharmacist about which foods or other drugs you should avoid when receiving a prescription for a new medication or trying a new over-the-counter drug.