Chemical Culprit in Grapefruit-Drug Interactions Identified

Note from the editor:

The mention of orange juice was not an error. In fact, orange juice was the "control group" in the study.

The study looked at blood levels of felodipine (Plendil; a blood pressure drug) after participants consumed 1 of 3 beverages:

1) grapefruit juice 2) furanocoumarin-free grapefruit juice. Furanocoumarins are compounds believed to be responsible for the drug-food interaction between grapefruit juice and some medications OR 3) orange juice

The researchers found that blood levels of Plendil were similar in people who drank orange juice or furanocoumarin-free grapefruit juice.

But levels of the drug were 3 times higher in those who drank regular grapefruit juice.

Thus, orange juice is safe to drink with blood pressure medication. However, you may want to avoid Seville oranges, as they are the only type of oranges to contain furanocoumarins.

We hope this clarifies all our reader questions.

I believe that there other medications that interact unfavorably with grapefruit juice. Can you tell me what they are? Thank You S. Golub MD

Two obvious questions remain. (1) How long does the FC effect last? (2) Can one lower the dose or frequency of taking a drug if one drings grapefruit juice?

How do I get replies to comments?

Why not take advantage of grapefruit's tendency to amplify the affects of drugs, by prescribing lower doses that MUST be taken with grapefruit? Seems like a way to reduce drug costs.

Why not take advantage of grapefruit's tendency to amplify the affects of drugs, by prescribing lower doses that MUST be taken with grapefruit? Seems like a way to reduce drug costs.

this explains why some drugs can make the pro time higher or lower, I cannot find any pain medication except tylenol that will not interfere with my coumadin... I never could understand why the same medication could work two ways either make the reading higher or lower...

Grapefruit juice can amplify the effects of a drug, but it can ALSO decrease the effect. The drug mentioned in this article is just one drug of many. It has not been exhaustively tested with all medications, but with what testing there has been, grapefruit juice was found to block absorption as well as increase it. So plain water is your best bet, and always following the instructions on the bottle.

Many people also don't get the best effects out of their medications because they don't take them as instructed. And many people get a prescription from the doctor, and don't ever even fill it. It could be cost-related, it is true. But for example, with antibiotics, people often stop taking the medication before they have taken the full course of treatment. So always read your instructions that should come with your medicines, or ask your pharmacist. Many bottles will even have warning stickers on them now, and I have seen grapefruit juice warning stickers on some medicines recently.