What do the drugs Percocet, Lipitor, and Wellbutrin have in common? It’s not what they do for you – one’s a pain med, another treats heart disease, and the third helps with depression. They’re not made by the same drug company, nor are they regulated the same way by the government. These drugs couldn’t be more different in the way they work, why they work, and how they’ve impacted our healthcare system. So what is it that they all have in common?

They, like many other drugs, can turn on you and cause you harm if you take them with grapefruit juice.

This is called the grapefruit effect.

Grapefruit and Your Body

Check the warning labels on your medications. Look at the folded up piece of paper with hundreds of lines of tiny text taped to the bag your pill bottles came in. Among the common warnings about dosing and side effects, chances are, you’ll see a warning that describes the grapefruit effect — it’ll tell you that you shouldn’t eat citrus fruits while taking your medication. This includes grapefruit, Seville oranges, limes and pomelos.

That’s an odd warning, don’t you think? Why would something as simple, natural, and delicious as a grapefruit cause so much trouble for someone taking heart medication?

grapefruit effect Pomelo Fruit Citrus Fresh Healthy Tropical
A pomelo

To put it simply, it’s a waste management problem.

When you take your medications, they’re supposed to do their job and then break down so you can pee them out. If your medications hang around in your body for too long, they can build up to the point where they become toxic and start hurting you. To help you out here, your liver contains enzymes that metabolize foreign substances, such as medications, before they cause harm. One family of enzymes, called CYPs, is responsible for breaking down the medications we take.

Grapefruits and other citrus fruits, though, contain compounds that stop CYPs from working. By halting CYPs’ work, the medications you take don’t get broken down, and instead, they’ll build up in your bloodstream and start damaging your body.

Who was the genius that predicted that something as innocent as the grapefruit could cause so much harm? Despite what you may think, the grapefruit effect wasn’t discovered through decades of intellectual discussion and careful experimentation. Instead, the link between grapefruit and medication was discovered by accident.

The Serendipitous Discovery of the Grapefruit Effect

Back in 1989, scientists were worried that drinking alcohol could affect how peoples’ blood pressure medicine worked. After all, doctors have known for some time that alcohol lowers peoples’ blood pressure. Combine that with a drug that’s designed for this purpose, and someone on a bender could lower their blood pressure too much and pass out.

To really understand how alcohol interacts with blood pressure medication, scientists decided to test it in an experiment. They gave people with high blood pressure medication meant to treat it, in combination with either an alcoholic drink or a non-alcoholic drink. The experiment was blind, meaning they didn’t want their volunteers to know whether or not they were drinking alcohol, so they needed to mask its taste so both drinks tasted the same. To do this, the researchers spiked the drinks with grapefruit juice.

Meanwhile, to be safe, the researchers gave everyone blood tests to measure how much medication was flowing through their bloodstreams.

So what happened? The alcohol did as expected: It lowered peoples’ blood pressure more than the medication did on its own. But when they looked at the volunteers’ blood samples, they found that there was a lot more blood pressure medication in their blood than they anticipated. They poured through their methods to figure out if they had made a mistake. Did they give their participants the wrong dose? Was there too much alcohol in the drink? No and no. After ruling out human error, they presumed that it must have had something to do with the grapefruit juice they were using to mask the taste of the drink.

They followed up their hunch with a new experiment with one lucky volunteer. On separate occasions, they gave their volunteer the blood pressure medication and a glass of water, and then they gave them the medication with a glass of grapefruit juice. And shockingly, when this person drank grapefruit juice after taking the medication, the volunteer retained five times as much medication in their blood than when they took the drug with water. Plus, the grapefruit effect lasted for half the day!

grapefruit effect
Why is Too Much Medication a Bad Thing?

The ramifications of the grapefruit effect vary depending on the drug. Sometimes, a drug that lowers your blood pressure or suppresses your immune system will become too powerful and put you in danger. But in most cases, doctors are worried that these drugs will overwhelm the enzymes and filters in your body (found in your liver and kidneys) to the point where these organs stop working. If your kidneys stop doing their job, garbage will build up in your body, causing all sorts of problems. You might have to go on dialysis, which is when a machine cleans your blood for you. If it gets worse, you might need a new kidney. It’s the same story with the liver.

Grapefruits can also decrease the effect of certain medications, such as the allergy medication Allegra. This is because grapefruits not only block CYPs, but they also block chemical transporters. These bridges allow chemicals to cross in an out of the cells in our body — just like bridges that span a river. Without a bridge to cross, Allegra can’t get into our cells to stop histamines from ruining our day.

So believe me when I tell you: as long as you have certain medications in your system, stay away from citrus. Check out the FDA’s list of medications that are subject to the grapefruit effect here to see if you need to remove grapefruit from your diet for the time being.


  • Ben Marcus

    Ben Marcus is a public relations specialist at CG Life and a co-editor-in-chief of Science Unsealed. He received his Ph.D. in neuroscience from the University of Chicago.

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