If you hanker for the tangy-sweet taste of grapefruit with your morning meal, better check the medicine cabinet first. Your citrusy obsession may interfere with your prescription medications.
Researchers have found that about six new drugs coming to market each year between 2008-2012 could cause a serious, potentially life-threatening drug-nutrient reaction if taken with fresh canned or frozen grapefruit, marinades and juice or sodas containing grapefruit or a few other citrus fruits. This was reported in a new study published in the Canadian Medical Association Journal.
The new additions dramatically expand the total number of drugs with serious grapefruit interactions from 17 to 43.
The researchers have known for a couple of decades now that grapefruit contains chemical compounds known as furanocoumarins that affect how some medicines are absorbed in the gastrointestinal tract.
Your body may absorb too much or too little of the drug, so your dosage will be off and that can spell trouble.
When some of these drugs are taken with even one serving of grapefruit, serious interactions can occur within hours.
The natural chemical in grapefruit is also found in Seville oranges which are used in marmalade, as well as in limes and Asian pomelos, but not in table oranges, according to the study.
The list of such drugs includes commonly used cholesterol-lowering statins such as Zocor and Lipitor, and blood pressure medications such as Nifediac and Afeditab, the study noted.
The Ottawa Citizen reported, “The anti-clotting agent clopidogrel (Plavix), which is taken to prevent a heart attack or stroke, doesn't work 'at all' if grapefruit is taken with it."
Grapefruit interactions can cause such high concentrations of some drugs that it can bring about acute kidney failure, lead to digestive tract bleeding, respiratory failure, bone-marrow suppression (in compromised immune systems), and even sudden death, the study said.
Grapefruit-interaction medications in question are all taken orally, have limited bioavailability — that is, only a small percentage of the active drug makes it into the bloodstream under normal circumstances — and all interact in the GI tract with an enzyme called CYP3A4.
Drug package inserts contain this information, the study pointed out, but many people, including physicians, may not be aware of its importance.
If you enjoy eating grapefruit or other citrus and take prescription drugs, it's advisable to ask your pharmacist or doctor if the drug has the potential for a food interaction.
In all, 85 drugs are known to cause a drug interaction when taken with grapefruit, but not all of these medications cause such serious adverse effects.
For some, the way grapefruit interacts with it can actually be beneficial.
A preliminary study published in Clinical Cancer Research shows consuming a glass of grapefruit juice makes the anti-cancer drug, sirolimus, three times more powerful without the side effects that typically accompany a higher dosage.
The FDA approved sirolimus to prevent rejection of a kidney transplant, but it can help some people with cancer.
The challenge for cancer patients is that sirolimus is so easily metabolized in the body that it leaves the bloodstream before it has had time to properly work. At higher doses optimal for producing anti-tumor effects, sirolimus causes significant gastrointestinal problems, most commonly nausea and diarrhea.
Dr. Ezra Cohen, a cancer specialist at the University of Chicago Medicine said in a news release that the researchers wanted to see if grapefruit juice could be “used in a controlled fashion to increase the availability and efficacy of sirolimus."
“This is the first study to use a cancer study to harness food-drug interaction,” the researchers wrote.
None of the 138 patients with incurable cancers in early stage trials had a complete response, but 30 percent of patients’ cancers did not advance. One patient saw his or her tumor shrink, which lasted for three years, the study said.
For more online information on food-drug interactions, visit the U.S. National Library of Medicine or National Institutes of Health Clinical Center Drug-Nutrient Interaction Task Force.
Lynette Summerill is an award-winning writer and Scuba enthusiast who lives in San Diego with her husband and two beach loving dogs. Besides writing about cancer-related issues for EmpowHER, her work has been seen in newspapers and magazines around the world.
Grapefruit-medication interactions: Forbidden fruit or avoidable consequences? David G. Bailey, George Dresser, and J. Malcolm O. Arnold. Canadian Medical Association Journal. First published online November 26, 2012, doi: 10.1503/cmaj.120951. Access online (requires subscription or pay-for-view)
Phase I Studies of Sirolimus Alone or in Combination with Pharmacokinetic Modulators in Advance Cancer Patients. Ezra E.W. Cohen et al. Clinical Cancer Research. Published OnlineFirst August 7, 2012; doi: 10.1158/1078-0432.CCR-12-0110. Abstract at:
“Grapefruit can interact with many drugs to cause severe effects or death: study. Sheryl Ubelacker, Ottawa Citizen. 28 Nov. 2012. Accessed online at:
Reviewed December 11, 2012
by Michele Blacksberg RN
Edited by Jody Smith