Tart, refreshing grapefruit juice is a healthful beverage filled with vitamin C. You should exercise caution in adding grapefruit juice to your diet if you are taking certain medications, however. This common breakfast food can increase or interfere with the effect of some medicines, and possibly even cause a dangerous drug interaction.
Grapefruit Juice and Drug Interactions
Scientists suspect that a chemical called furanocoumarin, found in sour oranges and tangelos as well as grapefruits, may be responsible for this fruit's interaction with certain drugs. Although it does not directly affect the action of drugs, furanocoumarin binds to an enzyme responsible for metabolizing medication. This can cause the drug to pass more easily into the blood, and potentially reach a dangerously high level.
Grapefruit Juice and Thyroid Medication
In the case of thyroid medication, grapefruit juice may affect the proper absorption of the drug, but not to any great degree. The most commonly prescribed thyroid medication, levothyroxine is used to replace the hormone naturally produced by a healthy thyroid gland. In a 2004 Finnish study testing the effect of grapefruit juice on the absorption of levothyroxine, the results revealed only a slight delay in the drug's availability to the body. This led the authors of the study to conclude that the minimal interaction between the juice and thyroid drug was of little clinical significance.
Grapefruit Juice and Blood Pressure Medication
Among the numerous medications that doctors prescribe for high blood pressure, some may be strongly affected by grapefruit juice, while others have little or no interaction with the juice. If you take felodipine or nifedipine for hypertension, for example, grapefruit juice could cause the medication's strength to be substantially increased. To avoid any potentially dangerous interactions, discontinue drinking grapefruit juice until you consult your physician. Other blood pressure medications, including verapamil, diltiazem and amlodipine, have either no reaction or minimal reaction with the juice. It's best to check with your prescribing physician to make sure.
Recommendations for Drinking Grapefruit Juice
Drinking only one glass of grapefruit juice can cause a nearly 50 percent reduction in the enzyme which regulates the absorption of medication. Additionally, the effect of the grapefruit juice on the enzyme is fairly long lasting, and it still evident even 24 hours later, according to the Harvard Medical School Family Health Guide. Check with your physician or pharmacist to learn if any of your prescribed medications are affected by grapefruit juice; if so, you should switch to a different breakfast beverage. At the very least, drink small amounts of grapefruit juice and allow the maximum possible time between juice consumption and taking your medication.
