Grapefruit is recommended by the American Heart Association as an excellent source of vitamin C, fiber and potassium. Unfortunately a chemical in grapefruit binds with a digestive enzyme that regulates how fast certain medications pass into the bloodstream. You could get dangerously high levels of a drug in your bloodstream if you eat grapefruit or drink grapefruit juice, even if it was the previous day. Although most drugs are unaffected, several classes of drugs are dangerous to use with grapefruit.
Hypertension -- Calcium Channel Blockers
Alan McKelvey, a pharmacist at the Frederick A. White Health Center, says one of the most significant drug interactions are with a class of drugs called calcium channel blockers, which are prescribed to treat high blood pressure. This class of drugs includes amlodipine, felodipine, nifedipine, nimodipine and nisoldipine. McKelvey pointed to studies in "The Lawrence Review of Natural Products" which have shown people who take Plendil, a brand name for felodipine, with grapefruit juice get four times the amount of the drug in their bloodstream as prescribed, leading to dangerous drops in blood pressure. Other drugs in the group have smaller increases, but still should not be used with grapefruit. A few calcium channel blockers, such as diltiazem, are safe to use with grapefruit.
High Cholesterol -- Statins
Another class of drug which reacts badly with grapefruit is the statins, also known as HMG-COA reductase inhibitors, which are prescribed for patients with high cholesterol. Simvastatin, lovastatin, atorvastatin are all absorbed more easily when combined with grapefruit juice and this can increase negative side effects from these drugs. Others statins such as fluvastatin, pravastatin and rosuvastatin experience little or no absorption increase from grapefruit.
Anxiety and Insomnia -- Benzodiazepines
A group of drugs called benzodiazepines are prescribed to relieve anxiety or insomnia. This class of drugs includes diazepam, triazolam, midazolam and buspirone. Increased absorption from grapefruit releases more of these medications into the bloodstream, which could produce excessive sleepiness, dizziness or other dangerous side effects.
Expert Advice
Dozens of other medications are affected by grapefruit. These include immunosuppressants, anti-convulsants, antidepressants, antihistimines, antifungals and psychotropic drugs. Always read the inserts with any medications you take to see if you need to avoid grapefruit. Tangelos and Seville oranges may the same effect because they have similar chemical makeup, so be careful with those as well. If you can't give up these fruits, ask your doctor for an alternate prescription. Note that only the generic names, not the brand names, of drugs are listed here. For example, if you take Valium you need to avoid grapefruit because Valium is a brand name for diazepam.
References
- The Harvard Medical School Family Health Guide: Grapefruit and medication - A cautionary note ; Feb. 2006
- Wright State University: Popular Natural Remedies, Part XII ; Alan C. McKelvey, R.Ph. ; 2003
- Mayo Clinic: Grapefruit juice - Beware of dangerous medication interactions ; Katherine Zeratsky, R.D., L.D. ; Nov. 2010
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