Nutrient-Drug Interactions: Be Informed!

  • Nutrient-drug interaction definition: some foods may alter blood concentrations of some commonly prescribed medicines and supplements — sometimes with dangerous consequences.
  • An example of an important nutrient-drug interaction may occur with grapefruit: the blood levels of certain drugs can increase more than five-fold when taken with large amounts of grapefruit juice and increase the risk of adverse effects. 
  • The possibility of life-threatening blood-clotting by blocking the effect of the common blood thinner called warfarin (Coumadin) with vitamin-K containing foods can have life-threatening consequences.

Fruit from paradise

Grapefruit (Citrus paradisi) is known as “fruit from the paradise” has health-promoting properties and is low in calories and provides an excellent source of vitamins A and C. Pink and red grapefruits unlike white or yellow varieties are a rich source of lycopene and beta-carotene — powerful antioxidants. Grapefruit has a low glycemic index (GI) of 25 and does not significantly affect blood sugar and insulin levels (unlike unsweetened grapefruit juice with a GI of 48 -similar to other juices which certainly can affect blood sugar and insulin). Grapefruits are an example of natural hybridization (cross-breeding) that is, a cross between two related species or cultivars. In the 18th century selective cultivation techniques crossed a pomelo and an orange to make this natural “genetic engineered” fruit we call the grapefruit (the name was given because it grows in clusters -just like grapes). Hybridization or cross-breeding has been going on since the beginning of human civilization and is a form of genetic engineering.

Grapefruit interactions

Grapefruits do however have a “darker-side” with an important nutrient-drug interaction making it important to consider what prescription drug you take along with grapefruit juice. Chemicals in grapefruit juice may interfere with normal metabolism of some prescription drugs but it usually takes a lot of grapefruit juice -about a quart. A critical enzyme called CYP450 3A4 in the small intestine is required for transformation of many common drugs into inactive chemicals. Grapefruit juice inhibition of this critical enzyme in some cases can lead to dangerously high drug levels of certain drugs and as a result, an increased frequency of adverse effects. Most notable are its effects on statins -popular cholesterol lowering drugs, anti-anxiety drugs (benzodiazepines), a class of blood pressure lowering drugs (called calcium antagonists) and a very potent immunosuppressant drug called cyclosporine used in bone-marrow transplantation and to prevent rejection of kidney, heart, and liver transplants.

Statin drugs

An estimated that 56 million American adults, or almost half those age 40 to 75, are now advised to take statins based on the most recent 2013 American Heart Association guidelines. Prior to 2013 the Centers for Disease Control and Prevention estimated that about one in four adults take statins -an incredible number making statins among the most prescribed medicine in the USA -so any potential nutrition-drug interaction is important to know about.

  • The consumption of large amounts of grapefruit juice, usually about 1 quart, may be associated with increased blood levels of the most common cholesterol lowering medication called statins such as Lipitor (atorvastatin), Zocor (simvastatin), and Mevacor (lovastatin). This interaction is important and can increase the incidence of statin drug side-effects such as muscle aches (myalgia) and weakness. In rare circumstances this interaction can trigger a very significant problem with muscle injury (myopathy) and serious kidney injury called rhabdomyolysis which can be life-threatening. Of all the statins, ZOCOR (simvastatin) has the greatest potential for this type of nutrient-drug interaction. However, it is unlikely that smaller amounts of grapefruit juice (one-half of a grapefruit or one 6 ounce glass of grapefruit juice) will have any clinically meaningful interaction and other statins (water-soluble statins) such as Crestor (rosuvastatin), Lescol (fluvastatin), and Pravachol (pravastatin) have no significant interaction with grapefruit juice.

More drugs          

Grapefruit juice may inhibit the metabolic pathways with some of the following:

  • Anti-anxiety drugs: Excessive drowsiness and prolonged sedation may result from consuming large amounts of grapefruit juice in combination with some tranquilizers (benzodiazepines) such as: Valium (diazepam), Xanax (alprazolam) or Versed (midazolam).
  • Blood pressure meds: an exaggerated blood-pressure lowering effect with consumption of large amounts of grapefruit juice and some blood pressure medications called calcium channel blockers: nifedipine (Procardia), amlodipine (Norvasc), or felodipine (Plendil) . This may account for an increased fall risk -especially important consideration for the elderly.
  • Anti-rejection medication: this interaction was also studied in kidney transplant patients who require the anti-rejection drug cyclosporine. Administration of cyclosporine with grapefruit juice compared with water induced a moderate, but significant increase in cyclosporine levels and an increased risk of cyclosporine side-effects like high blood pressure and even kidney damage.
  • Antibiotic: erythromycin also shares a possible interaction that may increase the risk for a potentially serious and life-threatening adverse effect that cardiologists encounter periodically. Erythromycin has been associated in some susceptible persons with a life-threatening form of arrhythmia (heart rhythm abnormality) called VT –which could cause sudden loss of consciousness and death. The mechanism is related to the prolongation of the QT interval (this is a finding measured on the EKG). A very long a QT is a well appreciated risk factor for life-threatening arrhythmia and increased blood levels of erythromycin with large amounts of grapefruit juice -can prolong the QT interval to dangerous levels.

Another common drug called warfarin (Coumadin) can be affected by some foods. Consuming more than one serving per day of foods rich in vitamin K (fresh kale, spinach, turnips, collard greens, Swiss chard, parsley) may block the desired blood thinning (anticoagulant) effect of warfarin -an important drug prescribed to prevent disastrous blood clotting. This nutrient-drug interaction may cause stroke in those who take this common blood thinner for atrial fibrillation (AF) -the common heart rhythm problem. This interaction may block the desired blood thinning effect of warfarin. When this interaction decreases the appropriate blood thinning effect of warfarin in someone with a mechanical heart valve there may be catastrophic valve failure requiring immediate medical attention.

Patients on a class of anti-depressant medications called monoamine oxidase-inhibitors (MAOI) need to avoid tyramine rich foods and supplements containing tyramine because of the risk of severe and a sometimes life-threatening spike in blood pressure called hypertensive crisis. Selegilin (l-deprenyl) is an example of a MAOI. Tyramine-containing products that may need to be avoided with some MAOI drugs include: air dried, aged and fermented meats, sausages and salamis, pickled herring, any spoiled or improperly stored meat, poultry, and fish, spoiled or improperly stored animal livers, broad bean pods (fava bean pods), aged cheeses, all tap beers and other beers that have not been pasteurized, concentrated yeast extract (such as Marmite), Sauerkraut and most soybean products (including soy sauce and tofu).


Consider talking to your healthcare provider about possible nutrient medication interactions -it may be important for you and your loved ones. Watch MedChefs for more relevant and important nutrient-interactions.