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Important Notice: GRAPEFRUIT JUICE...How NOT to Take a Pill

Important Notice: GRAPEFRUIT JUICE...How NOT to Take a Pill

Posted on October 25 2016

If you are swallowing a prescription drug, tablet or capsule, with a glass of fruit juice, make sure it’s not grapefruit juice. In fact, if you’re taking any kind of prescription medicine, check with your doctor before you go near grapefruit in any form.

The negative interaction of some medications with grapefruit has been known for a long time, but I never realized just how extensive the problem is or how serious a reaction can be until I recently came across a reference to a report in the Canadian Medical Association Journal (CMAJ).

The scientists* reporting in CMAJ concluded that more than 85 commonly prescribed drugs can react adversely with grapefruit, sometimes seriously. Some of the reactions include gastrointestinal bleeding, dizziness, urinary retention, in addition to others even more serious, and, also important, loss of a drug’s effectiveness.


Quoting the CMAJ Report’s Conclusion

“The current trend of increasing numbers of newly marketed grapefruit-affected drugs possessing substantial adverse clinical effects necessitates an understanding of this interaction and the application of this knowledge for the safe and effective use of drugs in general practice.”

Scientific Key Points of the CMAJ Report (Some over my head.)

  • Currently, more than 85 drugs have the possibility of interacting with grapefruit; of these drugs, 43 have interactions that can result in serious adverse effects.
  • Drugs that interact with grapefruit all have the following characteristics: they are administered orally, they have very low to intermediate absolute bioavailability, and they are metabolized by the cytochrome P450 3A4 enzyme (CYP3A4).
  • All sources of grapefruit and certain related citrus fruits can irreversibly inhibit CYP3A4 in the gastrointestinal tract; to prevent this interaction, affected drugs should not be consumed with any of these fruits during the treatment period, or noninteracting alternative medications should be prescribed.
  • Older patients have the greatest possibility of ingesting grapefruit and interacting medications and are the most vulnerable to the adverse effects.

Be safe. If you’re on a medical prescription, avoid grapefruit or check with your doctor.

* David G. Bailey BScPhm PhD, George Dresser MD PhD, J. Malcolm O. Arnold MB BCh MD

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