Antihistamines, anticoagulants, benzodiazepines (tranquilizers or sleep medications), calcium
channel blockers (blood pressure medication), cyclosporine (immunosuppressant drug used in
organ transplants), theophylline (asthma drug). Drinking grapefruit juice with a wide variety
of drugs ranging from antihistamines to blood pressure medication appears to reduce the
amount of the drug your body metabolizes and eliminates. The “grapefruit effect” was first
identified among people taking the antihypertensive drugs felodipine (Plendil) and nifedip-
ine (Adalat, Procardia). It is not yet known for certain exactly what the active substance
in the juice is. One possibility, however, is bergamottin, a naturally occurring chemical in
grapefruit juice known to inactivate cytochrome P450 3A4, a digestive enzyme needed to
convert many drugs to water-soluble substances you can flush out of your body. Without an
effective supply of cytochrome P450 3A4, the amount of a drug circulating in your body may
rise to dangerous levels. Reported side effects include lower blood pressure, increased heart
rate, headache, flushing, and lightheadedness.
Some Drugs Known to Interact with Grapefruit Juice*
Drug Class Generic (Brand name)
Antianxiety drug Diazepam (Valium)
Antiarrhythmics Amiodarone (Cordarone)
Blood-pressure drugs Felodipine (Plendil), nicardipine (Cardene), nimodipine
(Nimotop), nisoldipine (Sular), verapamil (Verelan)
Cholesterol-lowering drugs Atorvastatin (Lipitor), lovastatin (Mevacor), simvastatin
(Zocor), simvastatin/ezetimibe (Vytorin)
Immune Suppressants Cyclosporine (Neoral), tacrolimus (Prograf)
Impotence Drug Sildenafil (Viagra)
Pain Medication Methadone (Dolophine, Methadose)* This list may grow as new research appears.Grapefruit