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 have too much medicine in your blood. Having too much medicine in your blood increases your chances of having side effects.
Which medicines are affected by grapefruit juice?
Most medicines are not affected by grapefruit juice. And not all medicines for the health problems listed below are affected by grapefruit juice. But more than 50 medicines are affected by grapefruit juice. These can include medicines for:
- Abnormal heart rhythm.
- Blood clots.
- Erectile dysfunction.
- Heart attack or heart disease.
- High blood pressure.
- High cholesterol.
- Enlarged prostate.
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 must 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.footnote 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.footnote 2 Sometimes the effects of one glass of juice can last up to 3 days.
In many 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 your medicine?
The problems you may have from taking medicines that are affected by grapefruit juice depend on the kind of medicine you are taking and how your body reacts. 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 increased side effects.
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 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 to make sure they do not contain grapefruit, grapefruit juice, or grapefruit extract. Seville oranges (which are sometimes used in marmalade but not in orange juice), pomelos, and tangelos may also cause problems.footnote 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. This includes herbs, vitamins, homeopathic products, supplements, and over-the-counter medicines.
- Abramowicz M (2004). Drug interactions with grapefruit juice. Medical Letter on Drugs and Therapeutics, 46(1173): 2–4.
- Dahan A, Altman H (2004). Food-drug interaction: Grapefruit juice augments drug bioavailability—Mechanism, extent and relevance. European Journal of Clinical Nutrition, 58(1): 1–9.
- Pronsky ZM, Crowe JP (2012). Clinical: Food-drug interactions. In LK Mahan et al., eds., Krause's Food and the Nutrition Care Process, 13th ed., pp. 209–228. St Louis: Saunders.
Other Works Consulted
- Grapefruit (2011). In A DerMarderosian, J Beutler, eds., Review of Natural Products. St. Louis: Wolters Kluwer Health.
- Prior R (2006). Phytochemicals. In ME Shils, M Shike, eds., Modern Nutrition in Health and Disease, 10th ed., pp. 582–594. Philadelphia: Lippincott Williams and Wilkins.
- Whitney E, Rolfes SR (2011). Nutrient-drug interactions. Understanding Nutrition, 12th ed., pp. 599–603. Belmont, CA: Wadsworth.
Current as of: August 22, 2019
Author: Healthwise Staff
E. Gregory Thompson MD - Internal Medicine
Brian D. O'Brien MD - Internal Medicine
Adam Husney MD - Family Medicine
Theresa O'Young PharmD - Clinical Pharmacy
Current as of: August 22, 2019