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When Dr. David Bailey and his colleagues first published their findings that grapefruit juice could increase blood levels and effects of the blood pressure pill felodipine, many health care professionals were skeptical. But since that article in The Lancet in 1991, the evidence has become overwhelming that grapefruit can have a profound impact on many medications, not just felodipine. Dr. Bailey says that too many drugs do not carry appropriate warnings on their labels about the possibility of an interaction.
Grapefruit is not the only food that may interact with some medications. (Limes, pomelos and Seville oranges used in marmalade all share grapefruit’s potential.) Peppermint, licorice and charcoal-grilled meats could all alter drug levels or activity. High-fiber foods such as oat bran or bran muffins can interfere with absorption.
We welcome listener questions and stories about food and drug interactions they have experienced.
Guest: David G. Bailey, PhD, is Scientist at the Lawson Health Research Institute and Professor Emeritus at the Schulich School of Medicine & Dentistry at Western University (formerly the University of Western Ontario) in London, Ontario. His recent publication on grapefruit-drug interactions was in the Canadian Medical Association Journal. The list of medications is here.
The podcast of this program will be available the Monday after the broadcast date. The show can be streamed online from this site and podcasts can be downloaded for free for four weeks after the date of broadcast. After that time has passed, digital downloads are available for $2.99. CDs may be purchased at any time after broadcast for $9.99.

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  1. Bf
    Reply

    I recently had a bad experience taking Prevacid for Barrett’s esophagus. I think it interfered with my armour thyroid med and bupropion. My hair fell out and I was tired and depressed. My doctor urged me to stay on it but I quit when I started feeling suicidal. Within a week I started feeling better. Are there any studies on interactions or assimilation problems?

  2. Daniel Davila
    Reply

    I was just listening to the rebroadcast for the first time today on WBGO. I’m curious if there are any similar citrus fruits that also have drug interactions?
    You mentioned Bergamot as a possible ingredient in grapefruit that is responsible for the interactions. Bergamot oil is used to give Earl Grey Tea it’s distinctive flavor, are they any studies with specifically with Bergamot interactions?
    Incredible segment, I just became a fan.
    PEOPLE’S PHARMACY RESPONSE: Bitter orange, used to make marmalade, and limes also provoke a grapefruit-like reaction. I mentioned bergamottin, but Dr. Bailey tested Earl Grey tea and did not find that it caused a grapefruit effect.
    So glad you enjoyed the show. Keep listening!

  3. SalW
    Reply

    I listened twice to this very informative audio file to make sure I heard correctly, because I think you are in error when you made a statement not to drink milk while taking tamiflu. My daughter is a pharmaceutical rep for tamiflu and says this is not true. In fact, this is from the tamiflu website: “You can take tamiflu with or without food. There is less chance of stomach upset if you take it with a light snack, milk, or a meal.” Did I miss something?
    I now realize I should not eat grapefruit while taking losartan. Thanks to you and Dr. Bailey for such a complete list of interactions.
    Your radio show and newsletter provide such invaluable information for those of us trying to take control of the medications in our lives. Thanks!
    PEOPLE’S PHARMACY RESPONSE:
    Here is the study:
    J Pharm Sci. 2011 Sep;100(9):3854-61. doi: 10.1002/jps.22627. Epub 2011 May 23.
    Effect of milk on the pharmacokinetics of oseltamivir in healthy volunteers.
    Morimoto K, Kishimura K, Nagami T, Kodama N, Ogama Y, Yokoyama M, Toda S, Chiyoda T, Shimada R, Inano A, Kano T, Tamai I, Ogihara T.
    Source
    Faculty of Pharmacy, Takasaki University of Health and Welfare, Takasaki, Japan.
    Abstract
    We previously showed that oseltamivir, a prodrug of the influenza virus neuraminidase inhibitor Ro 64-0802, is a substrate of proton-coupled oligopeptide transporter (PEPT1), and its intestinal absorption in rats is markedly inhibited by administration with milk. To investigate the importance of PEPT1 for oseltamivir absorption in humans, and the characteristics of the drug-milk interaction, a crossover clinical study was conducted in healthy volunteers, who received 75 mg of oseltamivir with 400 mL of water or milk. Milk significantly reduced the maximum plasma concentration (C(max) ) and the area under the plasma concentration-time curve from 0 to 2 h (AUC(0-2) ) of both oseltamivir and Ro 64-0802 (oseltamivir, 68.9% and 34.5%; Ro 64-0802, 69.5% and 14.2%, respectively, vs. water), but had no significant effect on the apparent terminal half-life (t(1/2) ) or AUC(0-∞) . Urinary recovery of oseltamivir and Ro 64-0802 was significantly reduced to 77.5% of the control by milk. The early reduction of oseltamivir absorption might be through the PEPT1 inhibition by milk peptides. However, the extent of interaction in humans was limited as compared with that in rats, possibly because of species difference in the PEPT1 expression and its contribution. This might be the first report suggesting the clinical drug-food interaction via PEPT1.

  4. JMK
    Reply

    I really enjoyed this program, and am grateful to be able to print the table of interactions. The suggestion to take the Levothyroxin before retiring is very helpful; never heard that one before. That means I can take my supplements in the AM without worrying about the timing. I love grapefruit, but I guess I’ll have to do without, darn! Since I’m a person who learns better thru my eyes than thru my ears, I’d prefer a printed transcript to an audio.

  5. ktm
    Reply

    I take Armour thyroid when I get up. Then about 6 oz espresso (I let too much water in, but it’s still good). About an hour, sometimes longer, later I have a breakfast of mixed fresh fruits, plus a spoon of fish oil and a glass of metamucil with more supplements — garlic, glucosamine sulfate, probiotic, Cranactin, B complex. My thyroid levels are fine, so I think I’m ok. The idea of spending an hour after getting up (when I write) and NOT having coffee — unthinkable!

  6. Marianne
    Reply

    I take levothyroxine and have been having a very hard time with ups and downs and have had to change doses regularly. Recently I was told not to take the medication with any other vitamins and also that walnuts interfere with its absorption and I have been feeling better. Can you give me other guidelines about thyroid problems. Someone also mentioned fluoride as a problem.
    Thank you,
    Marianne

  7. ELE
    Reply

    I take 630 mg of calcium citrate plus D supplement daily. I do not take any drug prescribed medicine. I also take a multivitamin. I eat grapefruit almost every morning. Should I be concerned that the grapefruit can interact with the calcium supplement?
    PEOPLE’S PHARMACY RESPONSE: no.

  8. JMW
    Reply

    AFT, I’ve been advised not to eat or drink any ‘offending’ substances (coffee, calcium, iron, etc) for four hours before or an hour or two after taking my Synthroid. I’ve been waking up an hour early for years to take my Synthroid, and then turn over and go back to sleep for an hour so I can eat my breakfast and have my coffee “in peace”! I think as long as you are on the same schedule consistently, your doctor can keep you on the right dose for you by monitoring your TSH.
    PEOPLE’S PHARMACY RESPONSE: You are quite right that consistency is the most important factor. That way the dose can be adjusted for you.

  9. Pat
    Reply

    I take synthroid at night before I go to bed. I switched from milk to soymilk, going vegetarian. I don’t drink soy milk or have anything with calcium or magnesium at least 4 hours or eat anything 2 hours before I take the synthroid. Is that all right? I’ve tried to look it up on the internet and have not gotten anything that could be considered a good answer. On the other hand if you want to know how the order the drug online I’ve got some great URLs.
    I always check for interactions when taking new drugs but the soy milk has thrown me off. I don’t like not having an answer.
    Great show! I can always count on you for good advice.

  10. JKO
    Reply

    I’d appreciate knowing your response to AFT’s question above. Also, I’d like to know about the interactions between levothyroxine and walnuts (usually on my morning cereal) and levothyroxine and dietary fiber (isn’t that a big part of breakfast cereals such as oatmeal, Cheerios, and raisin bran)?
    PEOPLE’S PHARMACY RESPONSE: Levothyroxine doesn’t play well with dietary fiber. We’d suggest waiting at least half an hour after taking your levothyroxine before having breakfast and coffee. Better yet, take the thyroid pill at bedtime: http://www.ncbi.nlm.nih.gov/pubmed/21149757
    And for you and AFT, yes an hour is fine: http://www.ncbi.nlm.nih.gov/pubmed/18341376

  11. al
    Reply

    Are the potential interactions between grapefruit and medications immediate or build up over time or both?
    PEOPLE’S PHARMACY RESPONSE: Both.

  12. AFT
    Reply

    Listening to your show while drinking my morning coffee, I learn not to take my Thyroid Rx (T4 & T3) before drinking it. I normally wait about one hour — is that enough time?
    PEOPLE’S PHARMACY RESPONSE: Yes. An hour is fine.

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