Two antihistamines -- both no longer sold in the United States -- caused serious, even fatal side effects when combined with grapefruit. Newspapers, magazines and scientific journals do not report harmful interactions between Benadryl and grapefruit, according to a Lexis-Nexis search performed on June 10, 2011. However, this does not mean that interactions between grapefruit and Benadryl will not occur.
No Documented Interaction
The University of Maryland Medical School does not list grapefruit as a food to avoid while taking Benadryl, known generically as diphenhydramine. However, the People's Pharmacy says the effect of grapefruit on many medications remains untested. Substances known to interact poorly with Benadryl include MAO inhibitors as well as certain vitamins and herbs. Avoid medications that cause drowsiness or that also contain diphenhydramine.Before you take any prescribed or over-the-counter medication, ask your doctor or pharmacist about possible side effects and interactions.
Seldane and Hismanal
A 29-year-old healthy male died after combining Seldane, an antihistamine, and grapefruit. The man drank two glasses of grapefruit juice with Seldane, went outside to mow his lawn, and died of cardiac arrest. Seldane and Hismanal, another antihistamine linked to serious interactions with grapefruit, were taken off the U.S. market. Grapefruit can stop your body's CYP34A enzyme from metabolizing drugs. This can create a drug excess, making side effects more likely and more extreme. Some people -- and some medications -- are more affected by grapefruit than others.
Drugs Known to Interact with Grapefruit
The New York Times compiled a list of medications known to interact with grapefruit. The list includes some oral contraceptives, heart medications, antidepressants, anti-anxiety medications and cholesterol-lowering medications. Check with your doctor before combining grapefruit with medication.
CYP34A Enzyme
Everyone metabolizes drugs differently. Your body may naturally hold small or large amounts of the CYP34A enzyme that helps you metabolize drugs. "If you have a lot of this enzyme, you won't get much of certain drugs into your body. Therefore, taking grapefruit juice will have a big effect. If you have low amounts of this enzyme, you will already be absorbing higher amounts of drugs, and grapefruit juice will add little effect,'' Dr. Paul B. Watkins of the University of Michigan General Clinical Research Center in Ann Arbor told the Boston Globe. Consult your doctor before mixing grapefruit and medications in all circumstances.
References
- "The New York Times"; Experts Reveal the Secret Powers of Grapefruit Juice; Nicholas Bakalar; March 21 2006
- The People's Pharmacy Graedons' Guide to Grapefruit Interactions; 2002
- University of Maryland Medical Center: Diphenhydramine By Mouth; Jan 4 2010
- A Drug Recall: Seldane
- A Drug Recall: Hismanal
- "Daily Mail"; How That 'Healthy' Juice Could Give You Liver Failure -- Or Worse; Lynne Wallace; March 3 2009
