Is Grapefruit Affecting Your Medications?

Just one glass of grapefruit juice or half of a grapefruit can interfere with the breakdown of several commonly used oral medications. This results in greater levels of the medication in your blood than your doctor intended when writing the prescription. Specifically, "certain compounds in grapefruit juice inhibit the activity of cytochrome P450 3A4 (CYP3A4), which is one of the enzymes that metabolizes medications," explains Maria A. Summa, PharmD, BCPS, Assistant Professor of Clinical Pharmacy and Coordinator of Drug Information Services at the Massachusetts College of Pharmacy and Health Sciences. About 60% of drugs are broken down by CYP3A4.

Higher levels of drugs circulating in the bloodstream can enhance therapeutic effects or increase the risk of toxicity. Some of the many medications affected by grapefruit are listed in the table below. Please be aware that this is not a complete table. Talk to your doctor about the medications you are taking to see if they are affected by grapefruit. Those taken on a regular basis are more likely to be affected than something taken as a one-time dose.

Don't take this information to mean you should avoid grapefruit and its juice; both bring you a healthy dose of vitamins and phytochemicals. Rather, check with your doctor or pharmacist before changing your habits to determine how grapefruit can fit in with your medication regimen.