Q & A: Grapefruit vs. Medicine?

By AltMed1-Peggy  



I’d like to know what the deal is with grapefruit. I’ve always heard you’re not supposed to eat grapefruit with this or that meds, so now it’s pretty much banned in our household. But I like grapefruit! Any light you can shed on this is much appreciated.

— Jane



Although grapefruit is a great fruit from a nutrition point of view, it can cause a problem with medicines because substances in grapefruit interfere with an enzyme that helps your body break down drugs.

Researchers suspect one part of grapefruit that’s causing this interference is naringin, a flavonoid that gives grapefruit its characteristic bitter or tart flavor. (There may be other enzyme-blockers in grapefruit, too.)

Normally, when you swallow a drug, enzymes in the small intestine metabolize, or break down, the drug. If that process is blocked by something like naringin, you could wind up with too much of that medicine in your body.

In Grapefruit and Drug Interactions: What you need to know (2009), Nate Krall from the University of Wisconsin explains there are three main pathways by which grapefruit can interact with medicines:

1.  It can interfere with the tools your body uses to break down medicine and cause metabolism of the drug to slow down which lets too much of the medicine accumulate in your body.

2. It can disrupt  the way your body controls how much of the medicine is eliminated in your intestines and let too much of the medicine get into your bloodstream.

3. Or it can do the opposite – instead of causing too much medicine to build up in your body, it can interfere with a protein in your intestines that your body needs to be able to use the drug effectively. That means you wind up with too little of the medicine in your bloodstream, as if you’d taken a lower dose or not taken it at all.

The tricky part, according to the UC Berkeley Wellness Letter (May 2009, page 3), is this:  “The interaction happens fast and can last 24 hours or longer. But it’s highly unpredictable, varying from person to person and even from grapefruit to grapefruit.” Other citrus fruits that may have similar effects include Seville oranges (that are tart like grapefruit), pomelos and tangelos, UCBWL says.


Drugs known to be affected by this enzyme-blocking action include statins (used to treat high cholesterol), calcium channel blockers (used to treat high blood pressure), some antidepressants, anti-seizure medicines, an immunosuppressant, a drug used to treat HIV, and a medicine to treat abnormal heart rhythm. (For a detailed list and medical recommendations, see Grapefruit juice: Can it cause drug interactions? from the MayoClinic.com.)

Best bet:  If in doubt, check with your doctor or pharmacist and be sure they understand you’re asking about the interaction of grapefruit and medicines you take.  And ask if other fruits may also interfere with the specific medicines you’re taking — some research suggests other fruit juices may have a similar effect.

Want to know more?

Here’s where to find additional information:

* New reasons to avoid grapefruit and other juices when taking certain drugs, 19 Aug 2008, American Chemical Society (news release),  EurekAlert.org

* Grapefruit juice boosts drug’s anti-cancer effects, 20 Apr 2009, University of Chicago Medical Center (news release), Eurekalert.org

* Management of Grapefruit-Drug Interactions, August 15, 2006, American Family Physician

* Nutrition Journal, 2007 Oct. 30;6:33. Medicinal importance of grapefruit juice and its interactions with various drugs.  J. Kiani and S.Z. Imam.

© 2009, all rights reserved


One Trackback

  1. […] The same applies to those who prefer grapefruit – but be sure to check with your doctor before you increase the amount of grapefruit or grapefruit juice you consume because, despite its other benefits, grapefruit can interact with some medicines. (See our explanation in a previous Q & A column.) […]

Post a Comment

You must be logged in to post a comment.