Orange you glad you asked | Drug interactions with grapefruit and other citrus fruit


Our guest blogger, Jassu Dulai, Pharm.D., Drug Information Pharmacy Specialist, Beaumont Hospital, Royal Oak, talks about a recent study published in the Canadian Medical Association Journal saying the number of common prescription drugs that can interact badly with grapefruit is climbing.

When most of us pick up a medication from the drug store, we are not usually thinking about how certain foods or drinks may interact with it, especially when those foods are considered healthy.  A recently published study found that grapefruit juice can interact with more than 80 prescription drugs taken by mouth. What other foods/drinks should you be paying attention to?

Grapefruit juice interaction with medications was accidentally discovered in 1989 during a clinical trial. Researchers were investigating whether alcohol interacted with a blood pressure medication and used grapefruit juice to mask the taste of the alcohol.  Pharmacist, physicians and other health care professionals have known about this interaction for a long time and have been informing their patients about the interactions, including the serious outcomes which could occur.  So, why all of the sudden is this new study getting so much attention?  The study reports that the number of medications which interact with grapefruit juice is higher than expected, with only roughly 20 medications identified in earlier reports.

The drug-food interaction occurs because grapefruit juice reduces the level of CYP 3A4, an enzyme found in the liver and intestines, which metabolizes many medications. The amount of CYP 3A4 varies person to person, so grapefruit juice may affect people differently when they take the same drug. Medications also bind to CYP 3A4 at varying degrees, so some interactions lead to no clinically significant effects while others lead to dangerous levels of drug in the body.  The drug-food interaction can take place even when grapefruit juice is consumed 24-72 hours before the medication is taken, so simply taking the two at different times is not effective in preventing serious outcomes.

Remember that grapefruit juice is not the only food-drink to be on the look-out for while on medications.  Other citrus fruits such as Seville oranges and limes reportedly have the same effect as grapefruit juice. Other food/drink products that can have serious effects when taken with specific medications include (but are not limited to):

  • alcohol
  • caffeine
  • dairy products
  • cranberry juice
  • foods containing tyramine
  • herbal products
  • vitamins and supplements

While there are many more reports today which help raise awareness of drug-food interactions, there are still many potential interactions that have not yet been reported.  Always report any adverse effects you are feeling to your doctor. When picking up a prescription from the pharmacy, make sure to ask if there are foods, supplements or other drugs that you should avoid while taking your medication.  Also, keep your medications in their original container and read the instructions on them.

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