Drinking grapefruit juice is a medical no-no for people who take any of several widely prescribed drugs. The drink affects how the body metabolizes the medications. Now, researchers have pinned down the class of natural juice compounds that's responsible for the unwanted chemical interaction.
Researchers discovered around 1990 that grapefruit inhibits the enzyme CYP3A4, which participates in the metabolism of about half of all prescription drugs. Inhibition of that enzyme causes drugs to stay in the body longer, potentially overdosing the patient. Doctors subsequently advised many patients not to consumer the juice while using certain medications.
Paul B. Watkins of the University of North Carolina at Chapel Hill and his colleagues tested the idea that compounds called furanocoumarins, which are abundant in grapefruit juice but scarce or absent in most other citrus juices, are the metabolism-altering culprits.