Grapefruit juice and coffee

Originally Published: January 11, 2008
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Hey Alice!

I'm a student at CU, and I've heard that drinking coffee and grapefruit juice at around the same time can extend the effects of caffeine. Is this true? I know that grapefruits can increase the bioavailability of some drugs... what about caffeine? Is this at all dangerous?

Thanks. You're awesome, Alice!

Dear Reader,

What you've heard is generally true: the plant pigment, or flavanoid, naringin that is responsible for giving grapefruit its bitter flavor is also thought to slow down the breakdown of certain drugs in the intestines. Some of these drugs include calcium channel blockers, medications for HIV, allergies or high blood pressure, and caffeine. The prolonged digestion time means that these substances are not cleared out of the body as quickly as usual, leading to increased levels of the chemicals in the body. This is why many health care providers recommend that medications should not be taken with grapefruit juice unless the effects of the juice and specific drug interaction are known.

However, this does not necessarily mean it is dangerous to take every medication with grapefruit juice. Rather, it serves as more of a precautionary measure since we don't know for sure what will happen. Additionally, other researchers think that there is something besides naringin that causes the extended drug breakdown. Many speculate that is that that it is a group of several active chemicals in grapefruit that causes the effect or perhaps something else that no one has discovered yet.

If all of this is enough to make you give up the juice, don't despair quite yet. Although an unexpected and extended caffeine buzz may not be what you bargained for, you are not really at a risk for caffeine toxicity by combining coffee with grapefruit juice. Toxicity only occurs with extremely high amounts of caffeine consumption, equal to drinking about 150 cups of coffee within a limited time frame. If you want to play it safe, have you thought about switching to decaf coffee or try other types of juice in the morning? Could you also spread your juice and coffee consumption out during the day? Is leaving a few hours between drinking each beverage to make sure there is no coffee in your system by the time you have your juice, or the other way around an option for you? These are a couple of ways that you can have your coffee and drink juice too. 

Drink up!

Alice