Prescription Drugs and Grapefruit

How many of us take a prescription drug?  How many take multiple prescriptions?  And how many of us enjoy a morning glass of grapefruit juice because of the many health benefits it has?  As we age, high blood pressure, high cholesterol, and arthritis become more relevant theats.  I have managed to dodge the bullets so far although most of those ailments run in my family.  My curiosity of the link between prescription drugs and grapefruit was tweaked when a good friend sent me an email yesterday.  She had started a new drug for a nerve disorder.  Having entertained many guests and bed and breakfast clients over the July long weekend, she cooked, baked and served beverages many containing citrus.  And of course she ate and drank from all of the things she prepared.  After Canada Day she could hardly move which logically she thought was due to the busy weekend.  She realized that grapefruit might be the culprit when she awoke Monday morning to dimming eyesight.  She remembered a similar incident years earlier where her blood pressure had nose-dived and produced similar symptoms.  I remembered that my own parents, who take blood pressure medication, told me they could not drink grapefruit juice.  However, they were not sure of the reason why.  Allow me to elaborate!

The Chemical Culprit in Grapefruit

Studies have shown that even one glass of grapefruit juice can increase the levels of certain drugs in a person’s body to dangerous levels making it appear that the person overdosed on the medication.  A few other citrus fruits have similar effects on individuals taking certain prescription drugs:

  • Seville orange,
  • limes,
  • pomelos and
  • tangelos (a hybrid of the grapefruit and tangerine)

The culprit chemicals in these fruits are known as furanocoumarins.  Furanocoumarins are chemicals found in some plants that affect drug metabolism by affecting the amount of time it takes for a particular drug to be broken down in the body.

  • Our intestines contain an enzyme, cytochrome P-450 3A4.  This enzyme destroys a quantity of certain medications.
  • Drug companies increase the dosage level higher than what is required to compensate for the action of this enzyme.
  • When furanocoumarins are present in the intestine, drugs targeted by the enzyme cytochrome P-450 3A4, remain in higher concentrations, causing them to be absorbed into the bloodstream in higher quantities.


Interesting Fact

Many furanocoumarins are produced by plants as a means of defense against insects and mammals that would prey on them. These toxic phytochemicals cause severe burns when the victim is exposed to plant juices followed by exposure to sunlight.

Prescription Drugs that Interact with Grapefruit

Drugs that are affected by the consumption of grapefruit have the following characteristics:

  1. They are taken by mouth.
  2. Normally, the amount of drug that ends up metabolized by the body is quite low (this describes the bioavailability of the drug).
  3. They are metabolized by the cytochrome P450 3A4.
  4. They are more toxic to begin with.

These characteristics apply to a large number of prescription drugs taken by people around the world.  The drug profile provided by most pharmacies, in most cases, will indicate a reaction with grapefruit if it has the above characteristics.  Most pharmacists and doctors will also warn patients of any dangers associated with grapefruit interactions.  However, many patients taking these drugs are elderly, vulnerable and are being bombarded with a huge quantity of information regarding their illness.  In the case of my friend, she is dealing with multiple diagnoses so the large quantity of information she receives means some instructions may be missed or misinterpreted.

 Effects of Consuming Grapefruit and some Prescription Drugs

A comprehensive list of drugs that should not be taken with any grapefruit products or citrus fruits containing furanocoumarins can be found at WebMD.  These drugs include:

  • various blood pressure medications;
  • cholesterol-lowering drugs;
  • some antihistamines
  • psychiatric drugs including Valium;
  • impotence drugs including Viagra.

Because the consumption of grapefruit products can dramatically increase the amount of the drug in the bloodstream a number of side effects are possible depending upon the drug in question.  Drugs to lower blood pressure when consumed with grapefruit can result in the person suffering extremely low blood pressure causing dizziness, impaired vision and in extreme cases death.  Those taking statin drugs to lower cholesterol will have more of the drug staying in their body, putting them at risk for liver damage and muscle breakdown leaving them susceptible to kidney failure.  The effects of the furanocoumarins in grapefruit juice can be damaging whether consumed several hours before or several hours after taking the medication.  It is important that people on these drugs understand that grapefruit juice should be avoided completely while taking the medication.

As our population ages, and the numbers of individuals taking multiple prescription drugs is increasing.  As well, the number of drugs being developed that are metabolized by cytochrome P450 3A4 are also increasing.  Patients must be vigilant in making sure their doctor(s) and pharmacist are providing them with timely accurate information regarding the possible interactions with grapefruit and other common elements of our diet which may put them at risk and if possible, prescribing an alternative drug without the grapefruit interaction.

Prescription Drugs and Grapefruit- Beware!-


Bailey, David G., BScPhm PhD, George Dresser, MD PhD, J. Malcolm O. Arnold, MB BCh MD.  November 26 2012.  Grapefruit–medication interactions: Forbidden fruit or avoidable consequences?  July 9,2014

Reviewed by James Beckerman, MD, FACC.  October 30, 2013.  Grapefruit Juice: Is It Affecting Your Medication?  July 11, 2014

Thompson, Helen.  November 27, 2012.  More Drugs Cited As A Risky Mix With Grapefruit.  July 9, 2014

U.S. Food and Drug Administration.  January 27, 2014.  Grapefruit Juice and Medicine May Not Mix.  July 11, 2014



Transparent slice of grapefruit. Who knew the danger?


I would be interested in hearing any stories regarding your experiences with interactions of prescription drugs with grapefruit juice.  Feel free to leave your story in the comments below!

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