No doubt, grapefruit is a healthy food… it’s got few calories, little sugar and plenty of vitamin C and fiber.

But fifteen years ago, researchers discovered this citrus fruit plays havoc with certain medications, including some that lower blood pressure or cholesterol.

An unknown substance in grapefruit rushes drugs into the bloodstream, and can cause undesirable or even dangerous side effects.

Ever since, scientists have debated the identity of the substance.

A study published in a recent issue of The American Journal of Clinical Nutrition should settle that debate.

The culprit appears to be chemicals called furanocoumarins [furr-ann-uh-KOO-marr-inns], which may help plants repel hungry animals. Twenty varieties are found in grapefruit.

Previous research suggested these chemicals might interfere with medication. So the current study put this theory to the test.

Eighteen volunteers took a blood-pressure drug that’s affected by grapefruit. Then, in separate experiments, they drank furanocoumarin-free grapefruit juice, regular grapefruit juice and orange juice. Later, their blood was analyzed.

The modified grapefruit juice caused no adverse reaction, suggesting that furanocoumarins are indeed responsible for the drug interaction.

Researchers could use this finding in several ways.

First, there may be a market for furanocoumarin-free grapefruit juice.

More importantly, these chemicals could help patients get faster relief from medications.

So the great Achilles’ heel of grapefruit may prove to be useful after all.

It just goes to show the phrase “when life gives you lemons, make lemonade,” could apply to other citrus fruits as well.