There are now more than 85 drugs that may interact with grapefruit. The list includes statins (atorvastatin, lovastatin, and simvastatin), some antibiotics, cancer drugs, and heart drugs. Most at risk are older people who use more prescriptions and buy more grapefruit.

Grapefruit contains furanocoumarins, which block an enzyme that normally breaks down certain medications in the body. When it is left unchecked, medication levels can grow toxic in the body.

Other citrus fruits such asSevilleoranges (often used in marmalade), limes, and pomelos also contain the active ingredients (furanocoumarins), but have not been as widely studied.

The findings appear in theĀ Canadian Medical Association Journal.

This interaction can occur even if grapefruit is eaten many hours before taking the medication. For example, simvastatin, when taken with about a 7-ounce glass of grapefruit juice once a day for three days, produced a 330% greater concentration of the drug compared to taking it with water. This can cause life-threatening muscle damage.