Grapefruit juice and the fruit itself may be delicious and packed with vitamin C and potassium, but consuming them when taking certain medications can be problematic.
Darrell Willm, senior director of pharmacy services at Tidelands Health, says the thick-skinned citrus fruit has a property that can block the actions of CYP3A4, an enzyme that helps metabolize some medications. When that happens, more of the medication can enter your bloodstream and stay in your body longer, which can lead to potentially serious side effects.
Conversely, some studies have shown grapefruit having the opposite effect with some medications by limiting the amount of medication that enters the bloodstream – thus rendering it less effective. For example, that situation can occur with Allegra (fexofenadine).
As a result, the FDA has required warnings on some prescription and over-the-counter medications because of potentially dangerous interactions with grapefruit and grapefruit juice.

Here are some types of medications that have shown a potential interaction with grapefruit:

• Some statin medications to lower cholesterol such as Zocor (simvastatin) and Lipitor (atorvastatin)
• Some medications that lower high blood pressure such as Procardia and Adalat CC (both nifedipine)
• Some organ transplant rejection medications such as Sandimmune and Neoral (both cyclosporine)
• Some anti-anxiety medications such as buspirone
• Some corticosteroids that treat Crohn’s disease or ulcerative colitis such as Entocort EC and Uceris (both budesonide)
• Some medications that treat abnormal heart rhythms such as Pacerone and Nexterone (both amiodarone)
• Some antihistamines such as Allegra (fexofenadine)

“Not all medications in these categories interact with grapefruit juice,” Willm says. “And the severity of the interaction depends on the person, the medication and the amount of juice consumed. It is important to ask your doctor or pharmacist if consuming grapefruit may affect you or your specific medication.”

In addition to speaking with your pharmacist, physician or other qualified health care provider for guidance on whether you can consume grapefruit juice with a medication, Willm says it’s also a good idea to read the medication guide or patient information that comes with a medication or the drug facts label on your over-the-counter medication.

If you are supposed to avoid grapefruit juice with your medicine, be sure to check the labels of all fruit juices or drinks flavored with fruit juice to determine whether they’re made with grapefruit juice.
In addition, the FDA says people should avoid consuming tangelos, pomelos and Seville oranges (often used for orange marmalade) while taking medications that interact with grapefruit because these similar fruits may have a similar effect.