Grapefruit and Medicines: Can They Mix?

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Do you love that morning glass of grapefruit juice? If you take certain medicines, it might not love you back. The list of medicines known to interact with grapefruit has grown longer.

We've known for twenty years it's not safe to mix grapefruit and some prescription drugs. Eighty-five drugs are known or suspected to interact with grapefruit. More than half of them can cause very serious effects. These include dangerous heart rhythms, kidney damage, muscle damage, respiratory depression, and bleeding from the stomach or intestines.

Perhaps the most well-known example is muscle damage caused by some statins. These are drugs used to treat high cholesterol. Atorvastatin (Lipitor^®), lovastatin (Mevacor^®) and simvastatin (Zocor^®) are known to interact with grapefruit. The muscle damage results in muscle pain and tenderness. Breakdown products from damaged muscles may damage the kidneys.

Erythromycin, a common antibiotic, can cause a dangerous heart rhythm if taken with grapefruit. Nifedipine (Procardia^®), taken for high blood pressure, can interact with grapefruit to cause very low blood pressure. Hallucinations and seizures can result from combining dextromethorphan, a cough suppressant, with grapefruit.

At least ten chemotherapy drugs can interact with grapefruit. In these cases, the risk is a dangerous, irregular heart rhythm (Torsade de pointes), plus muscle damage. Some of these cancer drugs are erverolimus, dasatinib, and vemurafenib. Other types of drugs that interact with grapefruit include some pain relievers, sedatives, and drugs for prostate enlargement.

These problems can occur with grapefruit, grapefruit juice, even marmalade with grapefruit in it. Grapefruit inactivates an enzyme that metabolizes many drugs. Because grapefruit permanently prevents the enzyme from breaking down the drugs, the body must manufacture more enzymes. This can take 36 hours or more. For that reason, it doesn't help to stagger the timing of medicines and grapefruit.

For some drugs, a typical amount of grapefruit or juice can cause problems. For example, a single glass of grapefruit juice every day for three days caused the blood level of simvastatin (Zocor®) to increase more than 300 percent.

If you take a drug that interacts with grapefruit - and you really love grapefruit - there may be a work-around. Sometimes, another drug that has the same action can be substituted. Check with your doctor to see if that might be possible for you. In any case, don't stop taking a medicine without asking your doctor first.

What happens if you take grapefruit together with an interacting drug? It would be the same as taking an overdose of the medicine. Treatment would be the same as for an overdose.

When a prescription drug is filled, the label usually states if you should avoid any particular foods. If you aren't sure, ask your pharmacist or doctor.

And if you think you might be having a reaction between a medicine and grapefruit or grapefruit juice, call Poison Control right away. The 24-hour number is 1-800-222-1222.

Rose Ann Gould Soloway, RN, BSN, MSEd, DABAT emerita
Clinical Toxicologist