Be Aware of Grapefruit-Drug Interactions

by Dr. Julian Whitaker
Filed Under: Diet, General Health
Last Reviewed 02/06/2014

For many people, the day begins with a grapefruit or a tall glass of grapefruit juice. Nothing could be healthier, right? Perhaps, but if you’re taking prescription medications, what you don’t know about grapefruit might hurt you.
 
Though this fruit is an excellent source of vitamins, minerals, and fiber, it also contains a substance that blocks the liver’s capacity to metabolize certain drugs.
 
The interaction between grapefruit and drugs was accidentally discovered when Canadian researchers were exploring a possible interaction between alcohol and the blood pressure drug felodipine (Plendil), and grapefruit juice was used to disguise the flavor of the alcohol. Combining alcohol with the drug did not result in the predicted effects. Inexplicably, however, blood levels of the drug were three times higher than expected. After double-checking dosages and testing various combinations, they finally isolated the culprit: grapefruit juice.
 
Further research found an explanation for this unexpected effect. Several drugs are metabolized by a group of enzymes produced in the liver known as cytochrome P450. Natural substances in grapefruit inhibit the activity of one of these enzymes, CYP3A. This means that grapefruit essentially stops this enzyme from doing its job of breaking down certain chemicals. As a result, the blood levels of some drugs are higher and the drugs stay in the system longer, which increases risk of side effects and overdose.
 
To avoid these dangerous, and potentially fatal, consequences I recommend that you do the following:
 
  1. Check to see if your medication is on the grapefruit interaction list. For several years the grapefruit effect was believed to be limited to very few drugs: most calcium channel blockers, a couple of the statin cholesterol-lowering drugs, and several benzodiazepines (sedatives). But as more and more drugs have been tested, scientists have found that grapefruit interactions are fairly common (85 drugs have been identified so far). That said, research on grapefruit interactions is far from complete. If you’re unsure about any drugs you’re taking, talk to your doctor or pharmacist.
     
  2. If your drug is on the interaction list, do not eat grapefruit or drink grapefruit juice. Whereas most food-drug interactions can be avoided simply by taking the substances several hours apart, grapefruit may inhibit CYP3A for up to 72 hours. So if you have a glass of grapefruit juice on Monday, your body’s ability to metabolize your drug may be compromised until Thursday!
     
  3. If you consume grapefruit regularly and you’re taking any of the listed drugs, do not abruptly give up grapefruit. This could dramatically reduce or increase the blood levels of your medications, so discuss this with your doctor.
     
  4. Read labels carefully—mixed juices may contain grapefruit.
     
  5. Avoid tangelos and Seville oranges, which have effects similar to grapefruit.
Now it’s your turn: Have you ever been advised by your doctor or pharmacist to avoid grapefruit?
 

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