Drinking a glass of orange juice in the morning seems like a healthy idea—but if you’re taking prescription drugs, it could be just the opposite, according to a new study. University of Western Ontario professor David G. Bailey has shown that grapefruit and some other juices—including orange and apple—can decrease the absorption of certain drugs, in some cases destroying their effectiveness altogether.
In this study, Bailey recruited healthy volunteers to take the antihistamine fexofenadine (also known as Allegra), washed down with either one glass of grapefruit juice; water containing naringin, which gives the juice its bitter taste; or plain water. When the drug was taken with juice, only half of it was absorbed compared to when it was taken with water. Bailey says naringin blocked the drug from moving from the small intestine into the bloodstream.
It isn’t Bailey’s first foray into this type of research; he announced almost 20 years ago that grapefruit juice could boost levels of felodipine, a high-blood pressure drug in the body, causing it to concentrate in the blood stream. While controversial at the time, it’s now an accepted fact and even bears a name: the “Grapefruit Juice Effect.” (Today, nearly 50 drugs carry warning labels for this.)
But while that study showed grapefruit juice can boost absorption of some drugs, potentially leading to overdose, his latest research suggests it can have the opposite effect on some other medications.
Bailey’s press release notes that grapefruit, orange and apple juices have been proven to lower the absorption of anticancer agent etoposide; some beta blockers, which are used to treat high blood pressure; cyclosporine, which is taken to prevent the rejection of transplanted organs; and some antibiotics, too. But “we don’t [yet] know all the drugs affected,” he admits.
The bottom line: talk to your doctor before mixing juice and prescription medications. And when in doubt, drink water.