Overview

How does grapefruit juice affect medicines?

Grapefruit juice contains chemicals that can cause problems with how your body breaks down certain medicines. This can cause you to have too much, or too little, medicine in your blood. This increases your chances of side effects. Or it may prevent the medicine from working as well as it should.

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. This includes certain medicines for conditions such as allergies, anxiety, asthma, depression, high blood pressure, high cholesterol, and pain. But not all medicines for these problems or other health problems are affected by grapefruit juice.

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 this juice.

In general, the more grapefruit juice you have, the greater the possible effects. Even one glass of this juice—at any time of the day—is enough to cause certain medicines to work differently. Sometimes the effects of one glass of juice can last up to 3 days.

All new medicines are tested for problems caused by grapefruit juice before they are approved by Health Canada. Medicines that are affected by this juice must have warnings in their patient information sheets. When you get a new medicine, ask your pharmacist which foods to avoid while taking the medicine. Some medicines may also have warnings on the "food-drug interactions" section of the bottle.

If your medicine makes you feel sick, talk to your doctor. Also talk to your doctor if a medicine causes side effects that are unusual or that bother you.

What can happen if grapefruit juice affects your medicine?

If you drink grapefruit juice while taking medicines affected by grapefruit juice, the problems you may have depend on the medicine you are taking and how your body reacts. Some problems are mild. Other problems 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 have increased side effects.

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

How can you 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. Make sure they do not contain grapefruit or grapefruit juice or extract. Seville oranges (which are sometimes used in marmalade but not in orange juice), pomelos, and tangelos may also cause problems.
• Always read the warning labels for any medicine you take. If you have questions, ask your doctor or pharmacist.
• Tell your doctor if your medicine is making you feel sick. Also tell your doctor if it causes side effects that are unusual or that bother you.
• Tell your doctor and other health professionals about all the medicines and natural health products you take. This includes herbs, vitamins, and homeopathic products. It also includes supplements and over-the-counter medicines.