A new study identifies as many as 85 common medications that interact with grapefruit, and at least 43 such interactions can have serious side effects—including sudden death, kidney failure, and internal bleeding.

Writing in the Canadian Medical Association Journal, Lawson Health Research Institute's David Bailey—who first discovered that the bitter fruit can interact with drugs more than 20 years ago—and colleagues reported that the number of drugs that can interact harmfully with grapefruit has increased from 17 to 43 in the last four years.

The chemical culprits in grapefruits are called furanocoumarins, which deactivate an enzyme found in the small intestine and liver that breaks down various toxins and an estimated 50% of all drugs. When the enzyme doesn't function normally, medications may not degrade and instead circulate in the blood at higher levels than normal. This can effectively cause a medication overdose.

"Taking one tablet with a glass of grapefruit juice is like taking five tablets with water," Bailey says.

Popular drugs that interact negatively with grapefruit include various antibiotics, as well as drugs that treat hypertension, high cholesterol, and cancer.

The study notes that grapefruits are not the only fruits to cause problems with medications: Seville oranges, pomelos, and limes also contain the same family of disruptive compounds.

The study authors urge physicians to learn more about drug interactions with grapefruit (Thompson, "Shots," NPR, 11/27; United Press International, 11/27; Brown, "Booster Shots," Los Angeles Times, 11/27).