Grapefruit juice and fresh grapefruit 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.
Examples of some types of drugs that grapefruit juice can interact with are:
Grapefruit juice does not affect all the drugs in the categories above. Ask your pharmacist or other health care professional to find out if your specific drug is affected.
Too High or Too Low Drug Levels
Many drugs are broken down (metabolized) with the help of a vital enzyme called CYP3A4 in the small intestine. Certain substances in grapefruit juice block the action of CYP3A4, so instead of being metabolized, more of the drug enters the bloodstream and stays in the body longer. The result: potentially dangerous levels of the drug in your body.
The amount of the CYP3A4 enzyme in the intestine varies from one person to another, says Huang. Some people have a lot, and others have just a little—so grapefruit juice may affect people differently when they take the same drug.
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.