Grapefruit juice and fresh grapefruit are healthy as they have vitamin C and potassium. But they can interfere with the action of some prescription drugs, as well as a few non-prescription drugs. This interaction can be dangerous, says Shiew Mei Huang, acting director of the Food and Drug Administration’s Office of Clinical Pharmacology. With most drugs that interact with grapefruit juice, “the juice increases the absorption of the drug into the bloodstream,” she says. “When there is a higher concentration of a drug, you tend to have more adverse events.”
For example, if you drink a lot of grapefruit juice while taking certain statin drugs to lower cholesterol, too much of the drug may stay in your body, increasing your risk for liver damage and muscle breakdown that can lead to kidney failure. Drinking grapefruit juice several hours before or several hours after you take your medicine may still be dangerous, says Huang, so it’s best to avoid or limit consuming grapefruit juice or fresh grapefruit when taking certain drugs.
While scientists have known for several decades that grapefruit juice can cause a potentially toxic level of certain drugs in the body, Huang says more recent studies have found that the juice has the opposite effect on a few other drugs. “Grapefruit juice reduces the absorption of fexofenadine,” says Huang, decreasing the effectiveness of the drug. Fexofenadine (brand name Allegra) is available in both prescription and non-prescription forms to relieve symptoms of seasonal allergies. Fexofenadine may also be less effective if taken with orange or apple juice, so the drug label states “do not take with fruit juices.”