Grapefruit can Cause Unintended Effects

Drug interactions with grapefruit juice can lead to severe side effects

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) Grapefruit is a wonderfully healthy food, providing people with a rich source of vitamin C. However, compounds found in this fruit that can lead to potentially serious outcomes.

A recent consumer update press release from the FDA warns that compounds found in fresh grapefruit and grapefruit juice can act on an enzyme found in the intestines. This enzyme is an integral part of drug metabolism and can lead to potentially hazardous effects when combined with certain pharmaceutical and over-the-counter drugs..

If this enzyme cannot do its job properly, taking certain drugs can lead to toxicity because too much of the drug will enter the body.

"Ask your doctor about possible drug interactions with grapefruit."

The compounds in question are two chemicals in the class called furanocoumarins. One is the compound bergamottin, the other is a related compound called dihydroxybergamottin. These compounds prevent an enzyme called CYP3A4 from performing its proper function in digestion.

One of the jobs of CYP3A4 is to help the body process certain drugs. If the grapefruit compounds interfere with its ability to do its job, some of drugs you may be taking will not be broken down at the usual rate.

When manufacturers set the amounts of drug dosages, they are taking into account what CYP3A4 will be doing. If CYP3A4 is not working right, it may be possible for the person to end up with toxic levels of the drugs in their blood stream.

According to the FDA press release, drugs metabolized by CYP3A4 include statin cholesterol medications, such as Zocor (simvastatin), Lipitor (atorvastatin) and Pravachol (pravastatin).

Also on this list are some blood pressure medications, such as Nifediac and Afeditab (both nifedipine) and some immune-suppressant medications, such as Sandimmune and Neoral (both cyclosporine).

Anti-anxiety medications, such as BuSpar (buspirone), and some anti-arrhythmia medications, such as Cordarone and Nexterone (both amiodarone) are also have risk for interference from the grapefruit compounds.

Although these are not all the drugs that could be affected, they are some of the more common ones that could cause problems if taken with grapefruit.
The chemical bergamottin from grapefruit can cause another problem in the small intestines if a person is taking certain drugs. It can prevent transporter proteins from carrying certain medications through the body.

If these proteins can’t do their job, neither can the drugs that are transported by them. An example of a medicine that is transported by these proteins is Fexofenadine (Allegra), which is a common allergy medicine.

This information comes from a press release by the FDA, published in February of 2012.

Reviewed by: 
Review Date: 
March 7, 2012
Last Updated:
March 10, 2012