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:
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 the Food and Drug Administration (FDA). 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.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 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.