Think Before You Drink Grapefruit Juice

photograph of grapefruit
Courtesy of dullhunk via Wikimedia Commons

You follow the directions on your medication carefully, always taking the pills with the correct frequency and with or without food as directed. But have you discussed with your doctor or pharmacist whether ingesting grapefruit could cause an unintentional drug overdose?

A drug is normally metabolized in the gastrointestinal tract, but a liver enzyme called cytochrome P450 3A4 (CYP3A4) deactivates much of the drug so the body only absorbs about half of it. This process is taken into account when a doctor prescribes the necessary dose.

However, grapefruit, grapefruit juice, Seville bitter oranges (used in marmalade), limes and pomelos naturally contain chemicals called furanocoumarins. These furanocoumarins inhibit the CYP3A4 enzymes, causing the gut to absorb much more of the drug at a potentially toxic level. Sweet oranges, such as navel or Valencia, do not contain furanocoumarins.

This grapefruit-medication interaction was discovered back in 1989 by David Bailey, Ph.D., a clinical pharmacologist at the Lawson Health Research Institute. However, Bailey recently released an expanded list of medications affected by grapefruit in the peer-reviewed Canadian Medical Association Journal. The number of drugs that interact with grapefruit has significantly increased to more than 85 as new drugs have come on the market. More importantly, 43 of these drugs could interact with grapefruit and lead to serious side effects, such as kidney damage, blood clots, respiratory depression, abnormal rapid heart beats (torsade de pointes) and sudden death.

So it is important to carefully read the information leaflet that comes with your medications, as well as discuss with your doctor or pharmacist how your diet may affect your medication.

For more information about a potential drug overdose caused by ingesting risky citrus, please check out my KQED Quest blog.

Author: Jennifer Huber

As a Ph.D. physicist and research scientist at the Lawrence Berkeley National Laboratory, I gained extensive experience in medical imaging and technical writing. Now, I am a full-time freelance science writer, editor and science-writing instructor. I've lived in the San Francisco Bay Area most of my life and I frequently enjoy the eclectic cultural, culinary and outdoor activities available in the area.

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