“Are you crazy? You can’t have that grapefruit! It will interact with your drugs…” Yup! that’s what I hear at home when I cut up a grapefruit to enjoy its succulent acidity. I can pass on oranges, but grapefruits and pineapples are for me.

But, maybe they’re right! There’s a list of drug interactions with grapefruit- more than 80 of which I am aware, and maybe 40 of them are “severe”. Now, the question is whether this is CYA by the pharmaceutical industry or is it real…

You see, there is an enzyme in grapefruit (and a few other citrus that contains furanocoumarins) that stops our body from breaking down certain drugs. Which means that the drug can continue to circulate around our body at non-attenuated levels. Which means that the next day when we take a new dose, we could be overdosing on that drug.

One serious calamity manifests similarly to “torsade de pointes”. This is a ventricular tachycardia (arthymia) of the heart, which is seen on electrocardiograms as  long QT intervals (termed “LQTS”). This condition can also be inherited, but we are talking about one caused by drinking grapefruit juice that interferes with drug metabolism.

It seems that grapefruit juice interferes with the cytochrome P450 enzyme system (and also with P-glycoprotein). Many oral drugs are metabolized in the intestines or liver, once they initially pass through the organs, and become inactivated. Up until recently the only “almost complete list” of drugs so affected could be found on Wikipedia (http://en.wikipedia.org/wiki/Grapefruit_drug_interactions ) – but one had to be careful; this article (like many of them on Wikipedia ) is not well documented and can be altered at will.

Which may be why Drs. David Bailey and George Dresser (Lawton Health Research Institute, London, Ontario) decided to update their decades long research.  Bailey was among the first to find that grapefruit juice had this type of effect- it was able to mask the effects of alcohol, as reported in 1988.

Now, along with Dr. JMO Arnold, they have completed a literature survey to get to the bottom of this phenomenon. They will publish their results in the Canadian Medical Association Journal (available ahead of print if you are member). However, the list of drugs and the severity of their  interactions is available here, right now.

If you like grapefruit and are on drugs, it behooves you to check this list!

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