Oncolink.org had a good explaination for the potential interaction between chemo and grapefruit. See below.
Dear OncoLink "Ask The Experts,"
I am wondering if you clear up the mystery surrounding the contraindicated use of grapefruit/and or juice during chemotherapy?
Katrina Claghorn, MS, RD, Registered Dietitian at the Abramson Cancer Center of the University of Pennsylvania, responds:
Grapefruit can block the activity of an enzyme in the intestine that is involved in the metabolism of certain medications. Because the medications can't be broken down, blood levels may rise and become toxic. Drugs that are affected include cholesterol lowering medications, beta-blockers for high blood pressure, some psychiatric medicines, immuno-suppressants, and protease inhibitors. The only chemotherapy drug that grapefruit is definitely known to interact with is
Vincristine. However, there are concerns about the interaction of grapefruit with other chemotherapy drugs based on our knowledge of the way they function. If you regularly eat grapefruit or drink grapefruit juice, ask your doctor or pharmacist about possible medication and chemotherapy drug interactions. Other citrus foods and juices, such as orange juice, do not appear to interfere with medication metabolism.
Mayo Clinic has a nice chart displaying potential drug interactions.
http://www.mayoclinic.com/health/foo...rition/AN00413