Are you aware that grapefruit products (juice, whole fruit and sections) can react with some of the medications that you may take?  In our bodies, enzymes help us to metabolize or process medications. Cytochrome p450 (CYP450) comprises a large group of such enzymes which functions primarily in the liver and small intestines, and function in small amounts in the kidneys, lungs, and brain (1,2,3) These enzymes affect the way that some food and medications are metabolized.

how grapefruit interacts with certain medicationsYou may wonder what the name "cytochrome p450" stands for. Cyto means cell or body which contains a heme or iron pigment (the chrome and P). This enzyme absorbs light at a wavelength of 450 nm with carbon monoxide exposure. Thus, Cyto (cell) chrome (iron pigment) that absorbs light at a 450 nm wavelength. (4)

Different cytochrome p450 enzymes have further classifications. An example of one of the substrates is CYP3A4. Remember CYP is cytochrome. The 3 is the genetic family, the A is a genetic subfamily and the 4 is the specific gene member.

A potentially strong inhibitor of drugs that falls in the CYP3A4 category is grapefruit. (5) Predictions in the Canadian Medial Association Journal estimate that more than 85 drugs are known or are predicted to interfere with grapefruit due to this substrate. Forty-five of these drugs when interacted with grapefruit juice (or certain related citrus products including Seville oranges, limes and pomelos) can have very serious reactions. Navel, Valencia and some other sweet oranges do not fall in this category. (6) 

3 Examples of how Grapefruit Juice Effects Medications include:
1.    Repaglinide (Prandin) is an example from the diabetes medication list that interacts with grapefruit products. The interaction in this case may cause hypoglycemia. (7) 
2.    Simvastatin (Zocor) and some of the other medications in the statin classification are affected by grapefruit. It increases the levels of the drug in your blood thus increasing the risk of side effects. (8)
3.    Amlodipine (Norvasc) and some of the medications in the calcium channel blocker classification used for hypertension or high blood pressure and heart disease may also dangerously increase the level of the drug when consumed with grapefruit products. (8)

For a complete list of medications (including some specifically for diabetes, cholesterol and blood pressure) that have known reactions and potential reactions with grapefruit, visit the Canadian Medical Journal

View the U.S. Food and Drug Administration infographic depicting the interactions of grapefruit and medications. 

Many of my patients ask if it is safe to drink grapefruit juice and wait a few hours before taking a medication with a potential interaction. The answer is NO as the effect of grapefruit juice can last for more than 24 hours. The juice and the medication do not need to be consumed at the same time for a potential harmful reaction to occur. (9)

It is critical to note that people older than 45 years of age happen to take the greatest quantities of medication and typically buy the most grapefruit. (10) As one gets older the chance of interactions increase.  Ask your doctor and pharmacist about potential interactions that may happen with any of your medications. As you can see, reactions can be severely adverse and can easily be avoided by simply not eating or drinking grapefruit, Seville oranges, limes and pomelo products.