It’s long been known that grapefruit can dangerously boost the level of certain medications in the bloodstream. Now researchers have found that certain juices—including grapefruit—can do the opposite by lowering the body’s ability to absorb some drugs, sharply limiting their benefit.
Orange, apple, and grapefruit juice all can interfere with medicines, according to a team of scientists led by David G. Bailey, professor of clinical pharmacology at the University of Western Ontario. He’s the researcher who first identified the “grapefruit effect” nearly 20 years ago.
Presenting the new evidence at the American Chemical Society’s national meeting on Aug. 19, Bailey said healthy volunteers took a test drug, the antihistamine Allegra, with water and with juice. Taking the medication with juice cut its effectiveness by half.
Other research has also shown that fruit juices can reduce the performance of several medicines, including some antibiotics, certain types of beta blockers used to treat high blood pressure, certain cancer drugs, and medications used to prevent rejection after an organ transplant.
So is kicking an otherwise healthy juice habit the only way to go if you take multiple meds?
Not necessarily, says Sam Shimomura, a specialist in geriatric pharmacy and associate dean at Western University College of Pharmacy in Pomona, Calif. “If you have a fruit juice that you really like, consult your doctor or pharmacist to find out if it’s OK with a particular drug,” he says. Depending on the medicine and the juice, you may be able to time your pill-taking to avoid an interaction, or switch to another medicine that’s not affected.
According to Bailey, the drug-blocking potential of juices identified in the latest research lasts no longer than four hours.
Katharine Greider is a freelance writer in New York.