Grapefruit juice and drug interactions?

Originally Published: February 21, 2003 - Last Updated / Reviewed On: August 3, 2007
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Dear Alice,

I heard somewhere that drinking grapefruit juice with vitamins and/or prescription medicine is harmful. Is this true?

Dear Reader,

Hard to believe that a healthy drink like grapefruit juice would be a potential problem, right? Unfortunately grapefruit juice interacts adversely with certain, but not most, medications. Researchers believe that compounds in grapefruit juice suppress an intestinal enzyme that processes medications by means of the cytochrome p450 system, one of our bodies' detoxification processes. These compounds are not available, or are present in much lower amounts, in other citrus juices, such as orange juice.

So, what does this mean? When taken with grapefruit juice, the levels of these drugs become elevated up to as high as nine times their prescribed dosages in the bloodstream, increasing their potency and potential for harmful and even life-threatening side effects. Certain drugs prescribed for heart disease, blood pressure, and cholesterol, as well as some hormones, antihistamines, antibiotics, HIV medications, psychoactive drugs, and immunosuppressants, among other medication classes, cannot be taken for several hours before and several hours after drinking grapefruit juice, if at all. In addition to drinking commercially processed grapefruit juice, even eating grapefruit or drinking freshly-squeezed grapefruit juice may also interact with certain medications. Interestingly, intravenously administered medications appear to be unaffected by grapefruit juice.

As with any medications, it is important to talk with your health care provider and/or pharmacist about your prescription, over-the-counter, and herbal medications, their side effects, their contraindications (including whether or not grapefruit juice is safe to consume when using these drugs). If you are really into grapefruit, you may also need to discuss your history of consuming grapefruit and to see if the type or dosage of your medicine(s) needs to be adjusted accordingly. For those who would rather not avoid grapefruit juice, non-interacting drugs may be generally available as options.