The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 19 No. 5 • June 2016


Many, perhaps most, of you know that grapefruit juice can alter how prescription drugs are metabolized and, hence, could interfere with your medicinal drug regime. But what you may NOT know is that the flavonone naringenin, its bitter principal, is the source of these metabolic effects because naringenin inhibits the cytochrome P-450 enzymes, CYP3A4 and CYP1A2, found in the liver and supposed to metabolize these drugs for excretion. (Fuhr, 1993) If there is too much CYP3A4, the prescription drugs it metabolizes may be eliminated from the bloodstream too rapidly, leaving you deficient as compared to the amount you need for your drug treatment.

Naringenin is available as a dietary supplement and, indeed, it appears to have many potential benefits, as do flavonones in general. Still, the fact that it interferes with the function of the CYP3A4 cytochrome P-450 enzyme makes it risky to use if a prescription drug you’re taking is metabolized by that enzyme, such as theophylline and calcium channel blockers (such as nimodipine and verapamil). (Fuhr, 1993)

Sandy learned about this the hard way. She thought that small amounts of grapefruit juice (an ounce or less added to flavor a fruit juice drink) would be too small an amount to have a significant effect on any of the prescription drugs she uses (which includes theophylline), but it appears she was wrong. The prescription drugs she takes for restless legs may have been affected because she noticed that just as she began drinking small amounts of grapefruit juice, her restless legs became worse and when she discontinued it, the restless legs went back to where it started before the grapefruit juice. If that was due to grapefruit juice, naringenin would be expected to have similar effects.


  • Fuhr et al. Inhibitory effect of grapefruit juice and its bitter principal, naringenin, on CYP1A2 dependent metabolism of caffeine in man. Br J Clin Pharmacol. 35:431-436 (1993).

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