Until 1989, grapefruit was just another citrus fruit. It had a pronounced taste that some people found refreshing and others rejected as bitter. But then Canadian scientists published a surprising finding: taking the blood pressure pill Plendil (felodipine) with double-strength grapefruit juice could triple blood levels of the drug in some people.
The researchers had not set out to study grapefruit juice, so the discovery was almost incidental. They had chosen grapefruit juice because it masked the flavor of alcohol better than orange or apple juice did. They had planned to study the interaction of alcohol and felodipine and needed a way to give an inactive placebo that couldn’t be distinguished from the beverage containing alcohol.
That was just the beginning. During the 90s, investigators reported interactions between grapefruit and many different medications. Other blood pressure medications were also affected. So were cholesterol lowering drugs like Lipitor (atorvastatin), Mevacor (lovastatin) and Zocor (simvastatin).
Although we warned consumers about this interaction for years, most pharmacists and physicians found it more amusing than frightening. But by the end of the decade the FDA, drug companies and health professionals were all taking grapefruit interactions seriously.
Although there are now warnings on drug labels, there is a lot of confusion. We recently responded to a reader who hoped to save money on his cholesterol medicine by using grapefruit juice. We suggested that he might try this, but only if his doctor agreed to supervise: “Check with your doctor before trying this approach. We know one man who breaks his Lipitor in half, takes it with grapefruit juice and gets good results on his cholesterol tests.”
Many readers issued indignant howls in response: “Your answer regarding grapefruit juice and Lipitor was very dangerous. My 82-year-old mother has been on Lipitor for many years. ALL her medical doctors, including her cardiologist, have told us that she CANNOT have grapefruit juice!”
Another confused reader wrote, “I have been warned by pharmacists NOT to eat grapefruit or drink grapefruit juice as I am taking lovastatin because it reduces the drug’s effectiveness. I was eating grapefruit for weight control and gave it up. Yet Lipitor is a statin and your column suggest that grapefruit increases its effectiveness. Please clarify.”
Grapefruit raises blood levels of atorvastatin (Lipitor) by about 80 percent (British Journal of Clinical Pharmacology, Nov. 2005). Other drugs may be affected more strongly. This can increase effectiveness as well as the risk of side effects.
Anyone who would like to learn more about this fascinating field may wish to order our Guides to Food, Drug and Grapefruit Interactions. Please send $3 in check or money order with a long (no. 10) stamped (63 cents), self-addressed envelope: Graedons’ People’s Pharmacy, No. FJ-19, P. O. Box 52027, Durham, NC 27717-2027.
If people attempt to utilize the potential of grapefruit juice to increase the effective dose of a medicine, it must be done under medical care. Individuals vary in their susceptibility to this interaction and their doses need to be adjusted accordingly.