But the grapefruit compounds destroy the enzyme before it can go after the drugs, report Dr. Paul B. Watkins of the University of Michigan Medical Center and his colleagues. The team described their findings in the May 15 Journal of Clinical Investigation and the November Drug Metabolism and Disposition . Watkins is also with AvMax, Inc. in Berkeley, California, which is testing the effects of the compounds on various prescription drugs. Grapefruit's powers appear to increase over time. So if patients take their pills with the juice every day for a week, by the week's end the drugs will be even more potent than they were at the beginning of the week, the researchers report.
People differ in the amount of the enzyme that they have in their bodies.
The more enzyme a person has, the greater the impact grapefruit juice will have on them, Watkins says. It has no or little effect on a small number of people. Also, grapefruits vary in how much of the compounds they contain. The drugs effected by grapefruit include some sedatives and medications for high blood pressure, heart disease, allergies, AIDS, and organ transplants. Grapefruit juice may also interact with cholesterol lowering drugs and with a drug for gastrointestinal reflux.