Frequently Asked Questions (FAQ) Re: GJDI's

Take a look through these frequently asked questions about Grapefruit-Drug Interactions first. If you can't find the answer to your question, send an email to me at .

1. I don't drink grapefruit juice (GJ) but I do eat grapefruit pieces/sections or take grapefruit extract. Will this cause the same interactions with affected medication as the juice does ?

Recently, It has been shown that both grapefruit sections and an extract of grapefruit can cause interactions just the same way grapefruit juice can. The study was done with the blood pressure lowering drug felodipine (Plendil^Ž, Renedil^Ž). The blood levels of felodipine was increased equally whether it was given with juice, sections or grapefruit extract.⁷⁰ This has not been confirmed with any other medications, but it does seem reasonable that since grapefruit juice is made from grapefruit, the pieces and sections could cause similar drug interactions.

2. Will grapefruit juice or pieces affect physiological functions of my body such as: lowering cholesterol, worsening body odor, increasing liver enzymes, make me lose weight, cause drowsiness, dizziness or other effects ?

Unfortunately, my field of research is very specifically limited to interactions that occur between grapefruit and medications. I do not study the physiological and/or nutritional functions of grapefruit. All of my recommendations about grapefruit juice-drug interactions are based on original research articles in the medical literature. These articles do not examine physiological effects of grapefruit other than with regard to how it may affect drug metabolism. I am unable to give you an answer to these types of questions, and would request that I not be sent email regarding the physiological/nutritional function(s) of grapefruit. For this type of information, the best person to ask would be a dietitian. Click here for an online dietitian's website.

3. Will (the medication I am taking) interact with GJ ?

Not all medications have been studied with GJ, and many never will, based on their metabolic pathways in the body. To check if there is any information on my website regarding medication you take, return to the main page of my website, and use the search form at the bottom of the page. Type in the name of the medication you want to find out about, (generic or brand name is OK, but SPELLING COUNTS!) and if there is any information on my website about this medication, it will be found by the search engine.

4. How does GJ cause drug interactions with medications ?

OK, this is the short answer. Chemical compounds in GJ (primarily the compound 6'7'-dihrdroxybergamottin) are known to inhibit an enzyme system found in the small intestine that metabolizes some drugs prior to absorption into the bloodstream. This system is called CYP 3A4 and does play a role in the metabolism of certain drugs. Drugs that are affected by this interaction are metabolized less than usual when they are taken with GJ, allowing a higher amount to reach the bloodstream, and this will cause higher drug levels, sometimes with increases in clinical effects or side effects. GJ also affects a transporter called p-glycoprotein. The effects of this are less clearly defined, but p-glycoprotein is responsible for actively secreting some absorbed drugs back into the small bowel. For more detail, see the mechanism of action page.

5. I take a cholesterol lowering -statin drug known to interact with GJ. Can I have a glass of grapefruit juice in the morning, and then take my medication in the evening ?

This concerns the -statin drugs lovastatin (Mevacor^Ž), atorvastatin (Lipitor^Ž) and simvastatin (Zocor^Ž). Pravastatin (Pravachol^Ž), fluvastatin (Lescol^Ž) and rosuvastatin (Crestor^Ž) do not appear to be affected by GJ.

A study that was done by Merck (makers of Mevacor^Ž (lovastatin) gave the lovastatin dose in the evening after a single glass of GJ taken earlier that morning, and showed that the interaction was minimal, and that this practice could be done safely.⁵³

The above was only studied with lovastatin, but it is rational to assume that similar things would occur with the other -statins. However, this has not been directly studied.

The main risk with increases in blood levels of these -statin cholesterol lowering drugs is a condition called rhabdomyolysis: literally breakdown of red muscle. It can cause severe muscle pain, and kidney failure. It is rare, but not unseen with -statin drugs, especially when interacting drugs (certain antibiotics, certain heart medications) cause great increases in blood levels of the -statin drugs.

6. Do oranges and other citrus fruits cause the same interaction as GJ ?

This is an evolving area of research, but new evidence indicates that some related citrus fruits may cause drug interactions in a similar manner to grapefruit. These interactions are believed to be due to a group of chemical compounds that are specific to GJ and certain related citrus fruits. The most important of these chemical compounds is called 6',7'-dihydroxybergamottin. These interactions are not due to vitamin C or citric acid content. A variety of oranges called 'seville oranges' contain 6',7'-dihydroxybergamottin, and did seem to cause a similar drug interaction to GJ, but these are not used for commercial juice production and are only seen in the marketplace as the main oranges used in marmalade production. Evidence now exists for pummelos (pomelos) to cause similar drug interactions to grapefruit. More exotic grapefruit hybrids such as tangelos, have not been directly studied, and since they are not commonly seen in the marketplace, may never be studied. However, these products are genetically derived from grapefruit originally, and therefore may have potential for drug interactions.

7. I tried searching for (specified drug) with the search engine on the main page of this website, but no results were found matching my query. Now what do I do ?

First, re-check your spelling. Try entering the brand name (usually shorter, easier to pronounce) and then the generic name (longer, harder to pronounce). If you have a prescription that was filled outside of Canada or the USA, use of the generic name is best. You can search the internet to find the American brand name of your medication, and try entering that into the search engine. If all of these attempts fail, then it means one of two things:

1) There is no data regarding a grapefruit interaction with the medication you are searching for.

2) There is data regarding a grapefruit interaction, but it from a new article, and I have not added it to my website yet. I update the site regularly, but it may lag behind the medical literature by several months, due to delays in indexing services updating their databases, or delays on my part updating my website.

If you wish to search the medical literature for an interaction with grapefruit juice and your drug of interest, visit the online Pubmed website and enter the following search terms: "(drug of interest) and grapefruit" where (drug of interest) is replaced by the drug you are searching for. The generic drug name is preferred.