Grapefruit Interferes With Drug Levels

The following information piece was recently sent to medical toxicology physicians regarding the effect of grapefruits on medication metabolism and blood levels.  It is worth noting.

Drugs That Interact With Grapefruit on the Rise



The number of drugs that can be risky when taken with grapefruit is on the rise, largely due to the influx of new medications and chemical formulations, a new study shows.

As it stands, there are now more than 85 drugs that may interact with grapefruit. The number of drugs that may result in potentially fatal side effects when mixed with grapefruit increased from 17 to 43 during the past four years. This equates to more than six new potentially risky drugs a year.

The list includes some statins that lower cholesterol (such as atorvastatin, lovastatin, and simvastatin), some antibiotics, cancer drugs, and heart drugs. Most at risk are older people who use more prescriptions and buy more grapefruit.

Here’s what happens: Grapefruit contains furanocoumarins, which block an enzyme that normally breaks down certain medications in the body. When it is left unchecked, medication levels can grow toxic in the body.

It’s not just grapefruits, either. Other citrus fruits such as Seville oranges (often used in marmalade), limes, and pomelos also contain the active ingredients (furanocoumarins), but have not been as widely studied.

Grapefruit and Some Medications: Risky Business

Researchers searched the medical literature for articles on grapefruit and drug interaction using key terms. They also looked at prescribing information for recently approved drugs in Canada. Their findings appear in the Canadian Medical Association Journal.

Drugs that interact with grapefruit are taken by mouth. The degree of the grapefruit effect can vary. With some drugs, just one serving of grapefruit can make it seem like a person is taking multiple doses of the drug.

This interaction can occur even if grapefruit is eaten many hours before taking the medication. For example, simvastatin, when taken with about a 7-ounce glass of grapefruit juice once a day for three days, produced a 330% greater concentration of the drug compared to taking it with water. This can cause life-threatening muscle damage called rhabdomyolysis.

“Grapefruit and grapefruit products may interact with a broad class of medications ranging from cardiovascular to hormonal drugs,” says Tara Narula, MD, the associate director of cardiac care at Lenox Hill Hospital in New York City. “Some have more of an effect if you take them in close proximity to drinking grapefruit juice than if you space it out, but there can still be an interaction if you take the pill the night before or 12 hours before consuming grapefruit or grapefruit juice.”

“If you consume grapefruit juice and take medications, be careful,” Narula says. “If you need these drugs and there are not appropriate substitutes, you may need to limit or reduce your consumption of grapefruit juice and products.”

The researchers note that grapefruit interaction is specific to certain drugs and doesn’t necessarily affect an entire drug class. This can allow for grapefruit-friendly options.

Never stop taking prescription medication without first talking to your doctor. “Say, ‘I am on these medications, do I need to be careful about grapefruit juice?’”

If you are not taking any drugs that can interact with grapefruit, it is fine to eat and drink grapefruit and grapefruit products, which can be a healthy part of the diet, says Despina Hyde, RD. She is a registered dietitian at New York University Langone Medical Center.

But better safe than sorry. “Double check with your doctor or pharmacist, as it doesn’t really require a lot of grapefruit juice to produce a dangerous interaction,” she says.


Bailey, D.G. Canadian Medical Association Journal, published online Nov. 26, 2012.

Despina Hyde, RD, New York University Langone Medical Center, New York City.

Tara Narula, MD, associate director, cardiac care, Lenox Hill Hospital, New York City.

Source: Medscape November 2012

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