Drinking grapefruit juice to wash down some prescription medicines may be dangerous because the juice can raise blood concentrations of the drug beyond what the dosage calls for, researchers said on Tuesday.

Unlike other citrus juices, grapefruit juice inhibits one of the body's intestinal enzyme systems and can result in marked increases in serum levels of some prescription drugs, such as those to treat heart disease and control blood pressure.

Interactions between grapefruit juice and certain drugs -- which has been known but not extensively studied -- is particularly worrisome for the elderly who are more likely to take medications and may be inclined to drink calcium-fortified grapefruit juice, Mayo Clinic researchers Garvan Kane and James Lipsky wrote in this month's issue of the Mayo Clinic Proceedings.

Although some drugs are given with others to enhance their effects, grapefruit juice should not be used for this purpose because its impact can be unpredictable and potentially dangerous, they wrote.

Grapefruit juice does not pose a problem for those receiving medication intravenously, the report said.

(From China Daily)