It’s common to pick up a prescription and see stickers warning about the possible interactions with other medication. I always expect to see the little drowsy eye that cautions against drinking alcohol, or the glass of milk that directs you to take certain medicines on a full stomach. I would be a little surprised, though, if my medication came with a sticker that cautioned “BEWARE OF GRAPEFRUIT.”
A Citrusy Mystery
Since the early 1990s, drug researchers have known about the grapefruit effect, which can result in severe and potentially hazardous complications from mixing some medications with grapefruit. Plenty of drugs have citrus warnings to prevent patients from ingesting too much acid that could cause an upset stomach, but grapefruit is different. Originally, the scientists didn’t know what made grapefruit so special, but we now know that it contains chemicals called furanocumarins, which interfere with a specific enzyme in the intestines. This enzyme’s job is to break down certain drugs and flush them from the bloodstream, but when it’s inactivated, the drugs aren’t removed from the system properly. At best, grapefruit can diminish the efficacy of the medicine; at worst, the level of medication in the bloodstream can rise to toxic levels, leading to dangerous side effects. Furanocumarins occur naturally in grapefruits, pomelos, and Seville oranges, but conventional citrus fruits like lemons, limes, and regular oranges are safe.
The grapefruit effect doesn’t occur with every drug, but it does affect some popular and widely known medications such as cholesterol-reducers Lipitor and Zocor, anti-anxiety medications BuSpar and Valium, the immunosuppressant cyclosporine, and medications used to treat high blood pressure, irregular heartbeat, and HIV. Some believe the furanocumarins in grapefruit affect the estrogen in some birth control pills. Scientists are also monitoring anti-depressants Serzone and Desyrel, Viagra, Aricept, the breast cancer drug tamoxifen, Flomax, and the common allergy medicines Claritin and Allegra for potential interactions based on their molecular structure and the enzyme that breaks them down. Anyone who takes a medication that’s affected by grapefruit is usually urged to refrain from eating or drinking any of the fruit or juice at all, since the effect can occur even up to seventy-two hours before or after exposure.
