Grapefruit Juice and Drug Interactions: Answers to 5 Questions

A July 2010 article in the Wall Street Journal Online discussed the dangers of eating certain foods while you’re on particular medications. One of the most notorious situations is grapefruit juice and drug interactions—dozens of drugs are affected. And while this certainly isn’t “news” (the interaction has been known for more than a decade), food-drug interactions are a cause for concern among many patients.

• How does grapefruit juice cause drug interactions?
• Which medications are subject to grapefruit juice and drug interactions?
• Is the "Grapefruit Effect" limited to grapefruit?
• What can I do about grapefruit juice and drug interactions?
• What if I want to continue consuming grapefruit?

How does grapefruit juice cause drug interactions?
The grapefruit juice and drug interaction arises because grapefruit contains a compound called bergamottin, which blocks the action of an enzyme in the liver. (Cytochrome P450 3A4, in case you’re interested.) This enzyme is also involved in the metabolism of more than 30 different medications.
When this enzyme is blocked, your body can’t clear out the drug as it should, which means the drug can build up to dangerous levels.

Which medications are subject to grapefruit juice and drug interactions?
More than 50 medications are subject to a possible grapefruit juice and drug interaction. Drugs for blood pressure, blood clotting, and cholesterol control are among them. Here’s a complete list of drugs that interact with grapefruit juice.

Is the “Grapefruit Effect” limited to just grapefruit?
Other related citrus fruits may cause reactions similar to the grapefruit juice and drug interactions, depending on how much bergamottin they contain. Seville oranges contain a significant amount of bergamottin. They’re used to make marmalade and compote (but not orange juice) and their bergamot oil is used as the distinctive flavoring in Earl Grey and Lady Grey teas. Pummelos/pomelos have also been implicated in grapefruit juice and drug interactions.
Certainly there are other foods that can affect medications you’re taking, but grapefruit and grapefruit juice are the biggest culprits in drug interactions.

What can I do about grapefruit juice and drug interactions?
If you’re taking any of the medications on the grapefruit juice and drug interactions list, then you should avoid eating grapefruit or drinking the juice. But, and this is very important, if you’re already consuming grapefruit or grapefruit juice consistently, and you’re at a stable dose on your medication, then you should not stop consuming it.
Your doctor has calculated your medication dose based on your individual body and habits—including what you eat and drink. If your consumption of grapefruit has already been taken into account, then stopping suddenly could cause levels of your medication to fall too low, with possible negative effects.  

What if I want to continue consuming grapefruit?
I understand completely. Grapefruit and grapefruit juice are wholesome foods, with lots of health benefits. There’s even good evidence that regular consumption of grapefruit can help you lose weight. If you really love grapefruit, and intend to continue consuming it, then talk to your physician. He or she may be able to change your medication to one that doesn’t have a grapefruit juice and drug interaction.
As with anything, though, I recommend moderation. Among other things, grapefruit can affect the metabolism of some hormones, and there’s evidence that women who consume grapefruit often are at higher risk of contracting breast cancer. So, even if you’re not using any medications at all (and if that’s the case, then congratulations to you for staying so healthy), take it easy on the grapefruit.

Answers to more questions

Please remember that I cannot provide personal medical advice by e-mail or in this question-and-answer area. I can, however, provide guidance on what may help people in your situation. SS

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