Grapefruit juice and medications don't always mix, U.S. FDA warns

A new update from the U.S. FDA advises against taking certain medications with grapefruit juice. (HandmadePictures / Istock.com)

A new update from the FDA advises against taking some medications with grapefruit juice, as the fruit can interact with certain drugs.

Grapefruit juice can interact with certain drugs as "the juice lets more of the drug enter the blood," explains Shiew Mei Huang, PhD, of the US Food and Drug Administration, "When there is too much drug in the blood, you may have more side effects."

For example, drinking a lot of grapefruit juice when taking certain statin drugs to lower cholesterol can cause too much of the drug to stay in your body, increasing the risk of liver and muscle damage that can lead to kidney failure.

And as some people have more of the enzymes that break down drugs than others, grapefruit juice may affect people differently even when they take the same drug.

In addition, recent research has also shown that grapefruit juice can also have the opposite effect on some drugs, which use transporters rather than enzymes to move through the body. With these medications grapefruit juice causes less of the drug to enter into the bloodstream, therefore reducing its efficacy.

The FDA has now warned against eating grapefruit or drinking the juice while taking certain medications, especially those for high blood pressure or arrhythmia (irregular or abnormal heart beat), with a comprehensive list available on their website.

However, for those in doubt the FDA are advising patients talk to a healthcare professional such as their doctor or pharmacist, read the medication guide or patient information sheet that comes with prescription drugs, and read the Drug Facts label on OTC drugs, which will say whether grapefruit juices cause any problems.

The severity of the interaction between the juice and medication can also vary depending on the person, the drug, and the amount of grapefruit juice taken, and other fruits or juices such as Seville oranges (often used to make orange marmalade), pomelos, and tangelos (a cross between tangerines and grapefruit) may also affect drugs in a similar way to grapefruit juice.