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Unexpected Culprit – Is Grapefruit Affecting Your Drug Regimen?

In January of this year, we wrote about how herbal and dietary supplements can alter the metabolism of certain medications. St. John’s Wort was the supplement primarily discussed. However, it is not just herbal supplements that can alter drug metabolism and cause drug interactions; food can be a common offender as well.

This week we will be looking at the potential effects of a common fruit, grapefruit, on your medication regimen. Grapefruit and grapefruit juice may seem innocuous and simply part of an everyday diet. However, grapefruit has been observed with high levels of evidence to inhibit, or decrease the activity of, several enzymes that help process medication in our body. These enzymes or CYPs (pronounced SIPs) are responsible for flushing many drugs out of the body and for converting a few drugs to work at all. The enzyme grapefruit juice most heavily decreases activity of is CYP3A4. Per a review by “grapefruit juice consumption for 5 days caused a mean 62% reduction of … CYP3A4 and CYP3A5.”

What does this mean for you? Basically, drugs that are metabolized by CYP3A4, such as simvastatin (Zocor), can see significant increases in levels of drug in the body when taken with CYP3A4 inhibiting substances such as grapefruit. As a result of these increased drug levels, you may be more likely to experience side effects of that particular medication.

For more information and resources regarding CYP3A4 interactions and grapefruit:

  • Pharmacy Times provides an excellent list of medications that may be severely affected by this interaction, as well as a large list of other CYP3A4-metabolized medications (substrates), inhibitors and inducers.
  • The FDA has a great two-pager document for consumers that discusses these grapefruit interactions further.
  • Grapefruit and grapefruit juice, along with other food, herbals and supplements, are available in our
  • Ask your doctor or pharmacist if grapefruit consumption will impact your medication regimen. And always consult with them before changing your own medication regimen.

Grapefruit post graphic

Some of the foods and supplements available in the YouScript database.


We have received a lot of positive feedback on our articles regarding supplements and drug interactions. If you would like to see an article or want to know more about a particular supplement, let us know in the comments, reach out to us on
Twitter, or send us an email at info@genelex.com.  Ask your doctor or pharmacist if grapefruit consumption will impact your medication regimen. And always consult with them before changing your own medication regimen.

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