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Grapefruit Juice: Is It Affecting Your Medication?

A nutraceutical is a food or part of a food that allegedly provides medicinal or health benefits, including the prevention and treatment of disease. Grapefruit juice has been touted as containing many compounds that can reduce hardening of the arteries (atherosclerosis) and even the risk of cancer. Grapefruit juice can, therefore, be justifiably referred to as a classic nutraceutical. However, for many people taking certain medications, grapefruit juice might actually better be termed a "nutrapollutical!"

It turns out that grapefruit juice can directly or indirectly interact in important ways with a number of medications. This is especially important, because grapefruit juice is consumed by approximately one fifth of Americans for breakfast -- a time of the day when medications are also commonly taken.

Grapefruit juice blocks a special enzyme in the wall of the intestine that prevents many drugs from being absorbed into the body. When that enzyme is blocked, it is easier for those medications to pass from the gut into the body, raising the blood levels of these drugs. Abnormally high levels of some drugs can be dangerous and can lead to toxic side effects.

Amazingly, this remarkable food-drug interaction was discovered completely by accident over a decade ago. Researchers were investigating whether alcohol could interact with felodipine (Plendil) and used a solution of alcohol with grapefruit juice to mask the taste of alcohol for the study. Researchers discovered that blood levels of felodipine were increased several fold more than in previous studies. This increased blood level caused an increase in the effect and side effects of felodipine. Further research revealed that the grapefruit juice itself was actually increasing the amount of the study drug in the body.

Research about the interaction of grapefruit juice with drugs suggests that compounds in grapefruit juice, called furanocoumarins (or bergamottin), may be responsible for the effects of grapefruit juice. Researchers believe that furanocoumarins block the enzymes in the intestines that normally break down many drugs. One glass of grapefruit juice could elicit the maximum blocking effect, and the effect may persist for longer than 24 hours. Since the effects can last for such a prolonged period of time, grapefruit juice does not have to be taken at the same time as the medication in order for the interaction to occur.
Because waiting 24 hours between having grapefruit juice and taking -- sometimes daily -- medications, many people are advised not to drink grapefruit juice at all while also taking certain drugs.

The grapefruit juice-drug interaction can lead to unpredictable and hazardous levels of certain important drugs.

These are some medications with which grapefruit juice should NOT be consumed unless advised by a doctor:

  • Statins (cholesterol-lowering drugs): lovastatin (Mevacor), atorvastatin (Lipitor), simvastatin (Zocor, Vytorin)
  • Antihistamines: Ebastine
  • Calcium channel blockers (blood pressure drugs): felodipine (Nitrendipine, Plendil), nifedipine (Adalat, Procardia)
  • Psychiatric drugs: buspirone (Buspar), triazolam (Halcion), carbamazepine (Tegretol), diazepam (Valium), midazolam (Versed), sertraline (Zoloft)
  • Immune suppressants: cyclosporine (Neoral), (tacrolimus) Prograf
  • Pain medications: Methadone
  • Impotence drug (erectile dysfunction): sildenafil (Viagra)
  • Ant-HIV medication: saquinavir (Invirase)
  • Antiarrhythmics: amiodarone (Cordarone)

Alternatives exist for many of these drugs. If abandoning grapefruit juice is not an option, discuss the possibility of using an alternative with your doctor. And when you are starting a new medication, it is always a good idea to ask your doctor or pharmacist about any potential interactions between the new medication and foods, supplements, or other drugs you are already taking.

WebMD Medical Reference from MedicineNet

Reviewed by James Beckerman, MD, FACC on October 30, 2013
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