Chemicals in grapefruit can interact with a surprising number of medications, a fact discovered only in 1989. Grapefruit interferes with medications by blocking the action of an enzyme, CYP3A4, which reduces medication absorption. Blocking the enzyme allows larger amounts of a drug to enter your bloodstream, possibly causing an overdose. A single glass of grapefruit juice can decrease the effectiveness of CYP3A4 by as much as 47 percent, according to the Harvard Medical School Family Health Guide. Grapefruit does not react with other foods.
Statins
Grapefruit can affects some statins, medications classed as HMG-CoA reductase inhibitors that lower cholesterol, but not others. Statins most affected by grapefruit include lovastatin, sold as Mevacor; simvastatin, sold as Zocor; and atorvastatin, sold as Lipitor. Pravastatin, sold as Pravchol; fluvastatin, sold as Lescol; and rosuvastatin, sold as Crestor has little or no interaction with grapefruit products, according to the Harvard Medical School Family Health Guide. Signs of statin toxicity due to higher-than-normal levels of drug in your blood include abdominal pain and muscle aches. Severe muscle breakdown can lead to kidney failure in rare cases, a disorder known as rhabdomyolysis.
Brain-Altering Medications
Grapefruit can also interfere with several categories of brain chemistry-altering drugs used to treat symptoms such as anxiety and insomnia, including benzodiazapines such as Versed, used before many surgical procedures and Valium. Other benzodiazapines such as Klonopin and Dalmane do not interact with grapefruit. Anti-seizure medications such as Tegretol and antidepressants such as the selective seratonin reuptake inhibitor Zoloft may also interact with grapefruit. Excessive sedation could occur if you consume grapefruit while taking these drugs. Ambien and Haldol are not affected by grapefruit.
Calcium Channel Blockers
Calcium channel blockers help lower blood pressure. Certain calcium channel blockers, including felodipine, sold as Plendil and nifedipine, sold as Procardia or Adalat are most likely to interact with grapefruit. Verapamil, sold as Calan or Isoptin; diltiazem, sold as Cardizem; and amlodipine, sold as Norvasc have little or no interaction with grapefruit.
Immunosuppressants
If you've had an organ transplant, you take anti-rejection drugs known as immunosuppressants to prevent your immune system from rejecting your new organ. Cyclosporine, sold as Sandimmune, is the anti-rejection drug most likely to interact with grapefruit, but sirolimus, sold as Rapamune and tacrolimus, sold as Prograf, may also react with grapefruit. Toxic levels of anti-rejection drugs can cause kidney damage, high cholesterol levels, high blood sugars and high blood pressure.
Other medications
More than 50 medications can react with grapefruit products, according to the University of Rochester,although certain drugs are better known for causing reactions than others. Other medications associated with grapefruit interactions include the erectile dysfunction drug Viagra as well as the mycin antibiotics clarithromycin, erythromycin and troleandomycin.
References
- The Harvard Medical School Family Health Guide: Grapefruit and Medications: A Cautionary Note
- University of Rochester Medical Center; Grapefruit Juice and Medication Can Be a Dangerous Mix; January 2005
- UT Southwestern Medical Center: Post-Liver Transplant Education Packet
- "La Clinica Terpeutica"; Grapefruit Juice: Potential Drug Interaction; G. Palumbo, et al.; May-June 2005
- The People's Pharmacy; Grapefruit Interactions Can Be Tricky; December 2006
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