Like cranberry, grapefruit is another fruit whose juice has been a debatable addition to the warfarin diet. A popular breakfast fruit, grapefruit is known to be a good source of vitamins, fiber and other nutrients as well as containing antioxidant and immunity-boosting abilities. Grapefruit is also known to aid in lowering your weight or cholesterol.1Including grapefruit in your diet can be beneficial but the citrus has become well-known for interacting with different over-the-counter and prescribed medications.

The Grapefruit

An unintentional hybrid between the orange and the pomelo, the grapefruit was first documented in 1750 by a Welshman in Barbados. The citrus has been called by many names, including forbidden fruit, shaddock and paradise fruit, but grapefruit was so named because of the way it grew on tree branches in grape-like clusters.1 Since then, several varieties have been created including white, ruby red and pink, each with their own balance of sour and sweet.1 Grapefruit can be eaten alone, sweetened with sugar, mixed with various seafood dishes or topped with savory seasonings like cilantro or chili powder. 

While grapefruit provides a good source of vitamin A, folate and limonins, it is most known for its vitamin C content. Half a medium-size grapefruit can provide you with about 59 percent of your daily vitamin C needs.1 Vitamin C is important as it stimulates your body to produce white blood cells, possibly protecting immune cells as well as leukocytes, cells that produce antiviral substances. Red and pink grapefruit are also great sources of lycopene, second only to the tomato.1

Grapefruit and Your Body

It’s hard to believe that such a super fruit can cause such an issue, but grapefruit and grapefruit juice, even in concentrate, are known to interact with more than 50 different drugs.2,3 Some of the more common types of drugs grapefruit interact with include cholesterol-lowering statins, high blood pressure medications, allergy drugs and some drugs used to treat cancer. Grapefruit interacts with these medications in two ways:

  • First, compounds found in grapefruit called furanocoumarins can block specific enzymes your body uses to metabolize a drug. This can lead to an increase of the drug in your blood system, making it more likely for you to experience a side effect.2,3
  • Second, the grapefruit can also block the absorption of drug within the walls of your intestines, making you have less of the drug in your bloodstream. The drug can then become not as effective as it was intended.2,3

In both cases, the enzymes can stay blocked in your system for more than 24 hours. Full recovery from grapefruit’s effect can take up to 72 hours.3,4 The type of reaction that can occur depends on the drug as well as the levels of the drug that have been taken.3 However, it doesn’t take much grapefruit for a reaction to occur. According the Food and Drug Administration, reactions can occur with as little as one cup of juice or two grapefruit wedges.2

Grapefruit and Warfarin

It has been found that small amounts of grapefruit should have little effect on warfarin. Studies showed that people on warfarin showed no effect when they had up to three glasses (24 ounces) of grapefruit juice daily. Although, some case reports show increased INR associated with 50 ounces of grapefruit juice daily.4 Still, people taking warfarin should be cautious with their grapefruit consumption and other medications they may take. If you regularly enjoy grapefruit or grapefruit juice, speak with your physician about how it may interact with warfarin and other medications you take.

Other citrus with some of the same compound as grapefruit include oranges, pomelos, tangelos and limes.2,3  If you cannot bear to part with your morning citrus, speak with your physician about your medications that may be affected. Grapefruit has been shown to increase the risk of bleeding in people that take either apixaban or rivaroxaban, two other medications used to manage blood coagulation. For people on apixaban, it has even been suggested for elderly people to avoid grapefruit in general.4 Remember that as a person on warfarin, consistency in your diet is key to maintaining your target INR level.


  1. 1. Szaley, J. Grapefruit: Health Benefits and Nutrition Facts. Live Science. May 13, 2016. Retrieved from the website:
  2. 2. Mitchell, S. Why Grapefruit and Medication Can Be a Dangerous Mix. Consumer Reports. Feb 19, 2016. Retrieved from the website:
  3. 3. Anderson, L. Grapefruit and Medicines: A Possible Deadly Mix? Mar 20, 2017.
  4. 4. PL Detail-Document, Potential Drug Interactions with Grapefruit. Pharmacist’s Letter/Prescriber’s Letter. January 2013.



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