Grapefruit Juice and Medication

Overview

How does grapefruit juice affect medicines?

Grapefruit juice contains chemicals that can cause problems with enzymes that break down certain types of medicines in your intestines. When a medicine does not get broken down properly in the intestines, you can end up with too much medicine in your blood. Having too much medicine in your blood increases your chances of having serious side effects.

Which medicines are affected by grapefruit juice?

Most medicines are not affected by grapefruit juice. But more than 50 medicines are affected by grapefruit juice. These include medicines for:

• Abnormal heart rhythm.
• Allergies.
• Anxiety.
• Asthma.
• Blood clots.
• Cancer.
• Cough.
• Depression.
• Emphysema.
• Epilepsy.
• Erectile dysfunction.
• Heart attack or heart disease.
• High blood pressure.
• High cholesterol.
• HIV.
• Infection.
• Pain.
• Enlarged prostate.
• Stroke.

Not all medicines for the health problems listed above are affected by grapefruit juice. Ask your doctor how your medicines are affected by grapefruit juice and if you need to make any changes to avoid problems.

Is grapefruit juice safe for you?

If you regularly drink grapefruit juice, ask your doctor or pharmacist if any of your medicines are affected by grapefruit juice. If your medicine is making you feel sick or is causing unusual or uncomfortable side effects, talk to your doctor.

All new medicines are tested for problems caused by grapefruit juice before they are approved by Health Canada's Therapeutic Products Directorate (TPD). Medicines that are affected by grapefruit juice should have warnings in their patient information sheets. When you pick up a new medicine, your pharmacist will talk to you or give you written information about foods to avoid while taking your medicine. Some medicines may also have warnings on the "food-drug interactions" section of the bottle label.

In general, the more grapefruit juice you have, the greater the possible effects.¹ It has been shown that even one glass of grapefruit juice—at any time of the day—is enough to cause certain medicines to work differently than they are supposed to.² Sometimes the effects of one glass of juice can last up to 3 days.

In most cases, you may be able to have a glass of grapefruit juice without problems. Ask your doctor or pharmacist how much is safe for you.

What can happen if grapefruit juice affects my medicine?

The problems you may have from taking medicines that are affected by grapefruit juice depend on the kind of medicine you are taking. Some problems are mild, while others are more serious. In general, older people are more likely than younger people to have serious problems.

For example, if you are taking a medicine for high blood pressure, you may develop dangerously low blood pressure. If you are taking a medicine for high cholesterol, you may develop muscle breakdown problems or liver failure.

For more specific information on the kinds of health problems you could have if you drink grapefruit juice while taking a certain medicine, talk to your doctor or pharmacist.

How can I prevent problems?

You can take steps to avoid problems with grapefruit juice and your medicine.

• Before you take any medicine, ask your doctor or pharmacist if you can safely drink grapefruit juice.
• Read the labels on foods and natural health products to make sure they do not contain grapefruit, grapefruit juice, or grapefruit extract. You may also want to avoid Seville oranges (which are sometimes used in marmalade but not in orange juice), pomelos, and tangelos, because some studies have shown that they can also cause problems.³
• Always read the warning labels for any medicine you are taking. If you have questions, ask your doctor or pharmacist.
• Tell your doctor if you are having unusual or uncomfortable side effects from your medicine.
• Tell your doctor and other health professionals about all the medicines you are taking, both prescription and non-prescription (over-the-counter).

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Author:	Douglas Dana Caroline Rea, RN, BS, MS	Last Updated: January 3, 2008
Medical Review:	Anne C. Poinier, MD - Internal Medicine Theresa O'Young, PharmD - Clinical Pharmacist Andrew Swan, MD, CCFP, FCFP - Family Medicine
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