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.
The Chocolate Effect?
Grapefruit isn’t the only food that interacts poorly with medications. Anyone who takes an anticoagulant like Coumadin to prevent clotting should avoid eating any foods high in vitamin K, which encourages clotting and can reduce the drug’s effectiveness. That means staying away from green vegetables like broccoli, Brussels sprouts, cauliflower, kale, and spinach. People who take tetracycline for an infection should not consume large quantities of dairy, since calcium binds with the drug to form crystals that can’t be absorbed, and those crystals significantly reduce the effectiveness of the drug. Even licorice can adversely affect people taking certain heart medications, putting them at risk for a toxic complication.
One class of drugs is famous for having a lengthy list of potential food interactions. monoamine oxidase inhibitors (MAOIs) are old anti-depressant drugs that are sometimes prescribed when newer medications don’t work. They’re not often the first choice for most patients because MAOIs can react poorly with a compound in some foods called tyramine. Patients taking these meds cannot ingest foods high in tyramine, which include most kinds of cheese, yogurt, sour cream, cured meats and fish, avocados, bananas, raisins, soy products, fava beans, caffeine, red wine and chocolate. Because of its caffeine content, chocolate is also not recommended for people who take stimulant drugs like Ritalin or sedative drugs like Ambien, since the caffeine can enhance or lessen the effects of these drugs.
Besides food, countless things can interact with the absorption and efficacy of drugs—other medications, herbal supplements, a full or empty stomach, alcohol, and even sunlight. Women taking the osteoporosis drug Fosamax can’t even lie down for thirty minutes after taking their meds, or they risk experiencing painful acid reflux. The potential for interaction is the main reason that doctors need to know about everything a patient is currently taking. To avoid a serious complication, doctors can easily switch between medications or advise their patients to avoid certain triggers.
Doctors are familiar enough with drug interactions, including the grapefruit effect, to warn patients when they prescribe a medication that requires a vigilant diet or lifestyle change, so people whose medicines are affected by grapefruit, chocolate, or any other food probably already know about it. Information about potential drug interactions is also printed on the information sheet that comes with every prescription. Anyone worried that their daily healthy breakfast is going to wreak havoc with their prescriptions can relax, because it’s probably okay to enjoy that half a grapefruit. But I’ll probably use the grapefruit effect to justify ditching that healthy breakfast to eat Fruity Pebbles instead. You can’t be too careful, you know.