Q & A Library

Grapefruit juice contains compounds that interfere with the absorption and metabolism of a number of drugs, boosting their effects (and there is some concern that grapefruit itself might do the same). The compounds believed responsible for this effect are called furanocoumarins, which influence the action of an enzyme that works primarily in the liver and helps the body metabolize and eliminate drugs. In some cases, this means that more of a drug can enter the bloodstream and remain there longer. The drugs affected include:

• calcium channel blockers used to treat high blood pressure.
• non-sedating antihistamines such as Hismanal (astemizole).
• certain tranquilizers including Valium (diazepam), Xanax (alprazolam), and Halcion (triazolam).
• a number of cholesterol-lowering drugs, including Lipitor (atorvastatin), Mevacor (lovastatin) and other statins.
• immunosuppressive drugs used to prevent rejection of transplanted tissues organs and the antiviral agents used to treat HIV/AIDS.

The latest news on this subject comes from the researcher who discovered the grapefruit juice effect nearly 20 years ago. David Bailey, a professor of medicine and pharmacology at the University of Western Ontario, in London, Ontario, Canada, has now found that other juices, including orange and apple, may reduce the effects of certain drugs.

In a report to the American Chemical Society at its August 2008 national meeting, Bailey said his latest findings show that grapefruit, orange and apple juice can lower absorption of some drugs. Among them:

• the anti-cancer drug etoposide (Etopophos, Vepesid).
• certain beta blockers including tenormin (Atenolol) and talinolol (Cordanum), used to treat high blood pressure and prevent heart attacks.
• cyclosporine, which is needed to prevent rejection of transplanted organs.
• some antibiotics, including ciprofloxacin (Cipro), levofloxacin (Levaquin), and itraconazole (Sporanox).

Baily added that that more drugs may be involved. He also reported that healthy volunteers who took the allergy drug fexofenadine (Allegra) with grapefruit juice absorbed only half the amount as did volunteers who took the medication with water.

Bailey said that the best way to make sure you're getting the intended effects of the drugs you take is to wash them down with water. He also noted that a glass of water is better than a sip - it helps to dissolve pills.

Andrew Weil, M.D.