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Why is it so dangerous to take certain medications with grapefruit juice?

You’ve heard it as a warning amongst the volumes of side effects in TV commercials for prescription drugs. Or maybe your doctor has prescribed you a new medicine, and she made it a point to tell you to abstain from drinking grapefruit juice while on the medication…and then the pharmacist repeated the warning to abstain from the sourest of citrus fruit juices when you went to go pick up the medication. And it’s not just one drug, or even one kind of drug. The warning to not mix medicine and grapefruit juice is in effect for everything from cholesterol-lowering medications to heart pills to allergy medications to antidepressants. Just what is it about the nectar of a Ruby Red that interferes with sophisticated medicine? Isn’t fruit supposed to be healthy?

Of course fruit is healthy, but fruit is just as biologically and chemically complex as medications created over years and years in a laboratory. Grapefruit specifically carries chemicals called furanocoumarins.

They interfere with your body’s natural process of breaking down drugs (and sending the medicine where it needs to go). It can even negate the breakdown entirely. That doesn’t mean the medicine isn’t effective, it means that the body accepts the medication whole, and potently. It’s as if you’d be taking five pills instead of one…which is usually too many.

This is akin to an overdose of medication, and the damages are severe and many. It depends on the medication, but heart medications delivered in such a too-high dose could lead to blood clots or arrhythmia. Or, too much of a cholesterol-lowering drug could lower cholesterol too far.

By the way, these oft-repeated doctors’ orders don’t just refer to when you take your medicine. Whole grapefruit and grapefruit juice is off limits all day long, as those furanocoumarins stay in the body all day; just because you swallowed the pills with water, and then had a grapefruit juice later in the day, you’re still potentially messing with your meds.