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Will non-alcoholic beer affect
your Coumadin dose?
Does grapefruit really interact with medications? (See also....)
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Are there foods that interact with Coumadin even though they are low in Vitamin K?
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Can foods low in Vitamin K still affect my INR levels?
It's easy to get answers about health and nutrition! Just send your question by email to firstname.lastname@example.org and Dr. Harlan will respond to selected questions of general interest. Answers will be posted in the Ask Dr. Gourmet newsletter (sign up now!) and archived in the Ask Dr. Gourmet section of the website.
Can you clear up a rumor/urban legend? The story is that people who take Lipitor must not eat grapefruit. Consequently, most seniors who live in Sun City, AZ do not eat this wonderful fruit that grows in their back yard. It is my belief that if you eat the grapefruit in the morning, and then take the Lipitor at night, there should be no conflict. What do you think?
The interaction between grapefruit and some medications is not an urban myth. It is a fact.
This has been known for some time, but it wasn't until a few years ago that scientists identified the exact substance in grapefruit that causes the problem. We knew that furanocoumarins (a naturally-occurring substance found in grapefruit juice) had been found in laboratory tests to enhance the absorption of some medications, but lab tests are not the same as tests in human subjects.
A group of scientists created a furanocoumarin-free grapefruit juice to test against regular grapefruit juice and orange juice. Eighteen healthy subjects were recruited and given a medication that is known to be affected by grapefruit juice, along with a glass of either grapefruit juice, orange juice, or furanocoumarin-free grapefruit juice. Their blood was then drawn and analyzed for appropriate levels of the medication.
As they had suspected, it was indeed the grapefruit juice that contained furanocoumarin that had the most effect on medication levels. Sadly, furanocoumarin-free grapefruit juice is not available on the market, even though researchers noted that the furanocoumarin-free grapefruit juice tasted sweeter and less bitter than the regular grapefruit juice.
There's no research right now to confirm your theory that having the grapefruit in the morning and taking the medication later won't cause an interaction. While it is a good theory it's not proven and since these chemicals enhance absorption the grapefruit could very much change how much drug actually ends up in your body.
If you're on any medications, you need to be sure to tell your doctor what other medications or supplements you're using, as you can never be sure what might cause an interaction. Below is a partial list of the more common drugs that interact with grapefruit. The American Academy of Family Physicians has a fairly complete listing at https://www.aafp.org/afp/2000/0315/p1745.html, so if your medication is not on the list here on this page, check the AAFP's page to be sure.
Thanks for writing,
Timothy S. Harlan, MD, FACP
PS: Here's more information about grapefruit and medications.
|Type of medication||Name (Brand name in parenthesis)|
|Heart rhythm||Amiodarone (Cordarone)|
|High blood pressure
(calcium channel blockers)
Nifedipine (Adalat, Procardia)
Verapamil (Isoptin, Verelan)
|High blood pressure
Congestive heart failure (CHF)
|Emphysema / Asthma||Theophylline (Theo-dur)|
|Cholesterol lowering agent
|Immunosuppressants||Cyclosporine (Neoral, Sandimmune)
|Anti-HIV||Saquinavir (Fortovase, Invirase)
|Anti-seizure||Carbamazepine (Carbatrol, Tegretol)|
|Cough||Dextromethorphan (in many cough syrups and lozenges)|