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Hank: If you're like me, you probably try to tune out pharmaceutical commercials when they're on TV, but there's one drug warning that stands out: "Do not take this medication with grapefruit juice." But what's wrong with grapefruit juice? And what's in grapefruit juice that isn't in other citrus juices? Like orange juice, the normal one.

Grapefruit is full of a type of organic compound called furanocoumarin which interferes with the activity of an enzyme in your small intestine called CYP3A4. Problem is, that interference means your body will absorb more of certain medicines for things like high cholesterol, high blood pressure, and anxiety than it's supposed to. This enzyme's normal job is to chemically change certain potentially dangerous compounds before they can get into your bloodstream or liver. That way they're easier for your body to eliminate. But it also recognizes lots of different medications and deactivates them the way it would any chemical meaning that a large amount of the drug you take never actually makes it into your body to do its job. Except that the compounds in the grapefruit deactivate the enzyme, just one glass of grapefruit juice is enough to knock out nearly half of it.

So if the enzyme deactivates drugs and the compounds in the grapefruit deactivate the enzyme, that sounds like a good thing, more effective medications. No, it is not a good thing because one of the first things researchers do in a clinical trial is work out a safe dose. One that takes into account your body's attempts to remove toxins, including that enzyme. When your grapefruit juice gets rid of the enzyme you're suddenly getting way more of the drug than that safe dose. That can cause serious problems for your liver, which normally filters out these medications after they've done their job. You can also just have too much of the medication in you. If you drink a bunch grapefruit juice while you're taking blood pressure medication for example, your blood pressure could fall too far.

So if you take any meds but you're a big fan of grapefruit juice, you might want to talk to your doctor before you crack open a new bottle. Or just switch to orange juice, which tastes much better anyway.

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