Grapefruits and grapefruit juice interact with a number of medicines. There is a certain enzyme in the liver and small intestine called “P450, CVP3A4” which metabolizes much of what we eat. It’s one of many enzymes located throughout our digestive system. Grapefruit has a particular chemical in it called “furanocoumarin” which is a natural part of it. This chemical degrades or destroys some of the enzyme so that there’s not enough remaining to do its job of metabolizing what we ingest. It’s the case of one chemical destroying another—all perfectly natural and temporary as our body makes more enzymes to replace the lost ones. Research has discovered two additional biochemicals which may slightly influence grapefruit and certain drugs: P-glycoprotein and organic anion transport system receptors.

Important because of the effects on certain medicines we take, grapefruit increases the concentration of these medicines because the digestive enzyme is temporarily decreased, and this is not good. It’s not good because now the concentration of the medicines are increased too much in our bodies instead of eventually being decreased, digested and excreted as waste, which is the normal process. A single meal of 250 milliliter of grapefruit juice will increase the availability of these medicines for about 24 hours. (The same medicines are not affected when given intravenously.) It’s like taking too high a dose of your medicine—two or three times as much—which can result in adverse effects. Every medicine, without exception, can have its good and bad effects, and taking too much can increase your chances of having the bad effects.

Here is a list of the medications which are known to interact with grapefruit or grapefruit juice. Since science and research are continually evolving, the list is not comprehensive and will change with time, as well. The list of medicines is given in their generic names, so check carefully for the trade names and the generic names of your medicines because every medication has both.

Medications which interact with Grapefruit:

Amiodarone

Amlodipine

Astemizole

Atorvastatin

Buspirone

Carbamazepine

Cisapride

Cyclosporine

Diazepam

Felodipine

Fexofenadine

Lovastatin

Midazolam

Nicardipine

Nifedipine

Nisoldipine

Nitrendipine

Saquinavir

Sildenafil

Simvastatin

Tacrolimus

Triazolam

Verapamil

The bottom line is: grapefruit and grapefruit juice are “great” for you as long as you don’t ingest while being treated with certain medications. As always, consult with the appropriate physician if you have any questions. In future articles, I will list and comment on other drug-herb interactions I trust will be useful.

William H. Stager, DO, MS, MPH, FAAFP, FAMA, FAAO, FACOFP AOBNMM Board Certified: Neuromusculoskeletal Medicine/Osteopathic Manipulative Medicine. AOBFP Board Certified: Family Medicine. Medical Acupuncture. Clinical Professor, Department of Family Medicine, NSUCOM. Clinical Associate Professor, Department of Family Medicine, LECOM. Medical Director, Flagler Institute for Rehabilitation, Inc., 311 Golf Rd., Ste. 1100, West Palm Beach. To contact the author, call 561-832-1894.