Frequently Asked Questions

Q. Which drugs may interact with grapefruit?

A. Grapefruit can interact with some prescription medications either to increase the effect of those medications or to produce side effects. Something in grapefruit, perhaps a bioflavonoid, inhibits an enzyme, CYP 3A4, in the wall of the intestine, and this enzyme is important for the breakdown of hundreds of medications. When its effectiveness is compromised, blood levels of these drugs can rise and cause undesirable side effects. This happens only with drugs taken by mouth – not those given by injection or via skin patch, and the effect may last for as long as two days. If you are on any of these drugs you should discuss this with your doctor who will help you to monitor any possible interactions.

Drugs which may interact with grapefruit in some people:

• Some calcium channel blockers eg Felodipine (Plendil), Nicardipine (Cardene), Nifedipine (Adalat), Verapamil
• Some heart Drugs eg Amiodarone (Cordarone), Quinidine
• Some statins eg Atorvastatin (Lipitor), Simvastatin (Zocor) but not Pravastatin (Pravachol) and fluvastatin (Lescol).
• The blood pressure drug, losartan (Cozaar)
• Some sleeping Pills and anti-anxiety drugs eg Buspirone, (Buspar), Diazepam (Valium), Triazolam (Halcion).
• Some transplant drugs eg Cyclosporine, Tacrolimus and Sirolimus
• Some antidepressants eg nefazodone (Serzone) and trazodone (Desyrel)
• The antipsychotic, clomipramine (Anafranil)
• The cortosone-like drug, methylprednisolone
• The impotence (erectile dysfunction) drug, sildenafil (Viagra)
• The asthma drug, montelukast (Singulair)
• The Alzheimer’s drug, donepezil (Aricept)
• The breast cancer drug, tamoxifen (Nolvadex)
• The prostate drug, tamsulosin (Flomax)
• The antihistamines loratadine (Claritin) and fexofenadine (Allegra)
• Some oestrogens
• Some birth control pills
• The HIV/AIDS drugs, Ritonavir (Norvir), Saquinavir (Fortovase, Invirase)
• The epilepsy drug, Carbamazepine (Tegretol)