From the Canadian Medical Association Journal:

Many drugs can interact with grapefruit and certain other citrus, some with very serious adverse effects. Bailey and colleagues review the mechanism for these interactions and provide information on the most common drugs involved. Options to reduce the likelihood of such reactions include not eating these fruit or using alternative medications.

JoNel Aleccia at NBCNews reviews this important study:

If you kick-start your day with a glass of grapefruit juice, be careful.

Canadian scientists say the number of common prescription drugs that can interact badly with the tart citrus is climbing, with the potential for dangerous, even deadly, results.

Twenty-six new drugs that can cause serious harm when mixed with grapefruit have been introduced in the past four years alone, bringing the total to 43, said Dr. David Bailey, a clinical pharmacologist at the Lawson Health Institute Research Center in London, Ontario. That’s an average of more than six new drugs a year.

“What I’ve seen has been disturbing,” said Bailey, lead author on a study published in the Canadian Medical Association Journal. “It’s hard to avoid putting a drug out on the market that is not affected by grapefruit juice.”

Most (but not all) of the medicines studied are taken by adults rather than children.  Some are commonly used, such as some statins that treat high cholesterol and some cardiovascular drugs.  Aleccia explains how this interaction happens:

The problem is caused by an active ingredient in some citrus fruits, including grapefruit, limes and pomelos. Even the Seville oranges used in marmalades can trigger it. The fruits produce organic chemical compounds called furanocoumarins, which interfere with a human digestive enzyme.

That enzyme, called CYP3A4, helps metabolize toxic substances to keep them from getting into the bloodstream. Typically, that means the enzyme inactivates the effects of about 50 percent of all medications. Doctors adjust for that when prescribing drugs.

However, when the furanocoumarins in citrus inhibit that enzyme, the drugs can become concentrated in a patient’s system. In some cases, it can be like getting a triple or quadruple dose of medication, Bailey said.

Whole grapefruit, grapefruit concentrate, and fresh grapefruit juice were all identified as having the potential to interact with more than 85 drugs that were studied.  Some of the consequences were extremely serious, including acute kidney failure, respiratory failure, gastric bleeding, heart arrythmias, hypotension, and more.  Orange juice apparently does not interact with these medications.

Here is the list of medications found to be affected by grapefruit.

NBCNews article, including a video that summarizes the study with Dr. Nancy Snyderman on Today, is here.

Passing this information to the parents and grandparents in your lives might not be a bad idea (especially for those beloved “snowbirds” who winter in Florida).