Grapefruit seems like an innocuous addition to your diet, but it may cause serious medication interactions. Grapefruit enhances the actions of certain medications. If you take immunosuppressants that prevent organ rejection after organ transplant, you must avoid grapefruit altogether. Taking grapefruit with medications that increase the risk of developing blood clots may result in an even higher clotting risk.
Mechanism
Most medications go through the liver in a "first pass" that breaks down and eliminates some of the active ingredients in the drug perceived to be a threat to your body. Grapefruit contains substances that block the action of an enzyme found in the wall of the small intestine that helps break down medication. Exactly what substance in grapefruit causes this action is unknown, although more than one substance may be involved. A single glass of grapefruit juice interferes with many medications for as long as 72 hours, according to "Essentials of Nutrition and Diet Therapy" by registered dietitian Sue Rodwell Williams.
Grapefruit and Estrogen
An April 4, 2009 article published in the "Lancet" by Providence St. Peter Hospital physician Lucinda Grande reported on the case of a woman following the grapefruit diet who developed blood clots in the leg. The woman, who had been following the grapefruit diet and eating 225 g of grapefruit each morning for three days, was also taking an oral contraceptive, which has a known increased risk of developing blood clots. In addition, the woman was overweight, had an unusually narrow vein in her leg and had just completed a long car ride, also a risk factor for blood clots. While most people who eat grapefruit don't develop blood clots, in cases where several risk factors come together along with an increased consumption of grapefruit, unpredictable consequences may occur, hematologist Trevor Baglin warned.
Grapefruit and Warfarin
If you take blood thinners such as warfarin, grapefruit may produce the opposite effect and decrease -- rather than increase -- the risk of blood clots, but also increase the risk of hemorrhage. Because grapefruit potentiates the effects of warfarin, which acts as an anti-coagulant, your blood may not clot as well as it would normally.
Considerations
Grapefruit is not generally a dangerous food, although it may cause health problems under specific conditions if you're taking certain medications. Ask your doctor if grapefruit will have a serious effect on any of the medications you take.
References
- MayoClinic.com; Deep Vein Thrombosis; August 2009
- "Essentials of Nutrition and Diet Therapy;" Sue Rodwell Williams; Mosby; July 2002
- Medical News Today; Grapefruit May Have Raised Blood Clot Risk In Unusual Case; April 2009
- Harvard Health Publications; Does Grapefruit Juice Affect Aspirin?; Anthony L. Komaroff, M.D.; June 2007
