By the way, doctor: Is it okay to drink grapefruit juice, as long as I don't take my statin at the same time?
Q. I've been advised not to take my statin drug, simvastatin, with grapefruit juice. But is it safe to take the medication at night and then drink grapefruit juice in the morning?
A. Grapefruit is a great low-calorie source of vitamin C, fiber, and other nutrients. But we've known for several years that this citrus fruit and its juice can interact adversely with many prescription drugs, including some of the statins that are widely used to lower cholesterol. (There's some evidence that pomelos, a fruit that resembles grapefruit, and Seville oranges, which are used in making marmalades, have a similar effect.)
Grapefruit contains compounds that interfere with digestive enzymes that break down (metabolize) various drugs — especially the enzyme CYP34A, which is part of a large family of drug-metabolizing enzymes called cytochrome P450. This increases the amount of drug absorbed and thus the amount in the bloodstream. Other chemicals in grapefruit alter the activity of proteins responsible for transporting some drugs through the wall of the intestine. This also boosts drug absorption and blood levels of the drug.