Grapefruit and grapefruit juice are often recommended as part of a healthy diet. But if you enjoy this citrus fruit and are taking certain prescription drugs, the mixture can cause problems.

Grapefruit products can increase the amount of some drugs in the bloodstream. This may cause heart palpitations, headaches and seizures.

What happens?

An enzyme called CYP3A4 helps some drugs get absorbed properly. But ingesting grapefruit products can cause a drop in CYP3A4. So, there might not be enough of the enzyme to break down certain drugs. That means too much of a drug stays in the bloodstream.

Some medications that interact poorly with grapefruit are:

• Statins (to lower cholesterol)
• Antiarrhythmic agents (to correct heart rhythm)
• Immune system suppressants (often used after organ transplants and for autoimmune disorders)
• Calcium channel blockers (to lower blood pressure)
• Protease inhibitors (to treat HIV/AIDS)
• Certain anti-anxiety and antihistamine drugs

The interaction between some drugs and grapefruit may last up to 72 hours. So scheduling certain medications around any grapefruit intake is not really possible.

Most other citrus fruits do not block this enzyme, except for tangelos and Seville oranges.

Can other foods affect your medicine?

Many drugs can be affected by what you eat and when you eat it. Some medicines are easier to tolerate when taken with food. Food can delay or decrease absorption of others. To fight this, some drugs should be taken on an empty stomach.

Here are some tips to help you determine the best ways and times to take medication.

• Read the prescription label on the container and ask your doctor or pharmacist if you have questions.
• Read all directions, warnings and precautions on labels and packages.
• Take most medicines with a full glass of water unless your doctor says otherwise.
• Most medicines should not be stirred into food or have the capsules taken apart. It can change the way a drug works.
• Don't take vitamins at the same time as medicine. Some drugs don't interact well with vitamins and minerals.
• Don't mix medicine into hot drinks. Heat may affect how the drug works.
• Don't take medicine with alcohol.

Talk to your doctor and pharmacist about possible interactions between prescription medications, dietary supplements and over-the-counter drugs.

To learn more about potential drug interactions visit the myOptumHealth drug guide. This resource includes information on specific medications, such as proper dosage, possible side effects and how a drug works in your body.

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External Sources American Academy of Family Physicians. Drug-food interactions: How grapefruit interacts with certain drugs. Accessed June 10, 2008. University of Florida Institute of Food and Agricultural Sciences. Using medications safely: Interactions between grapefruit juice and prescription drugs. Accessed July 11, 2008. American Academy of Family Physicians. Food-drug interactions. Accessed June 10, 2008. Stump AL, Mayo T, Blum A. Management of grapefruit-drug interactions. American Family Physician. 2006;74(4): 605-608.

This article was reviewed and updated 08-01-2009.