Can Your Breakfast Harm You?


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Can Your Breakfast Harm You?

October 15, 2014


It’s supposed to be the ultimate healthy food.  It’s supposed to be good for you.  Could it harm you, though? A review published in a recent issue of the Medical Letter lists many medications that can interact with Grapefruit Juice.


How does grapefruit juice interfere with medications?

Grapefruit juice contains furanocoumarins. These substances, along with other components in the juice can interact with medicines you take.


There are some important enzymes in the body that help break down and metabolize medicines.  Some of these are called CYP3A4.  Grapefruit juice acts in the intestines to interfere with CYP34A and other enzymes.  This means that if you are taking something like lovastatin (Mevacor), and drinking a lot of grapefruit juice, the amount of Mevacor could build up in your system because your body cannot eliminate it.  And even after you stop drinking the juice, the effect lingers for a few days.


The effect varies depending on how much you drink.  The more you drink the more the enzymes in your intestines are inhibited. This effect occurs with both fresh and frozen grapefruit juice.  And though the studies have all been done with juice, the effect will occur with eating the fresh fruit as well.


Are there other fruits that I should be careful about?

What about other fruits and fruit juices?  The furanocoumarin, bergamottin is found in pomelos, Seville (sour) oranges, and lime juice.  Again, the problem is dose related so if you have a very small amount, it probably is not of major concern.   Sweet oranges and tangerines are not found to inhibit the enzyme CYP3A4.  There is no information on lemons or oil of Bergamot (used in Earl Grey tea).


Which medicines interfere with these fruits and fruit juices?

So, which medicines should you watch out for if you drink a lot of grapefruit juice or eat a lot of grapefruits?  The list is too long to print but a few of the important ones to consider include benzodiazepines, dextromethorphan, fexofenadine (Allegra), “statin” drugs, and silfenadil (Viagra).  No one has studied dietary supplements and “herbal” preparations so take them at risk.  Be sure to talk to your doctor and find out if your medicines interact with grapefruit juice.



The Medical Letter. Volume 46 (Issue 1173) January 5, 2004.


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