This happens in two ways. One is that grapefruit can block an enzyme which metabolizes medication. If the drug is not metabolized, then the level of the drug in the blood can become too high leading to an adverse effect. The other effect is that grapefruit can block the absorption of drugs in the intestine. If the drug is not absorbed, then not enough of it is in the blood to have a therapeutic effect.
One whole grapefruit, or a glass of 200 mL (6.8 US fl oz) of grapefruit juice can cause drug overdose toxicity. Drugs which are incompatible with grapefruit are typically labeled on the container or package insert. People taking drugs can ask their health care provider or pharmacist questions about grapefruit / drug interactions.
- The World's Healthiest Foods; Grapefruit. The George Mateljan Foundation. Article
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- Mitchell, Steve (19 February 2016). "Why Grapefruit and Medication Can Be a Dangerous Mix". Consumer Reports. Retrieved 4 May 2016.
- Bailey, D. G.; Dresser, G.; Arnold, J. M. O. (2012). "Grapefruit-medication interactions: Forbidden fruit or avoidable consequences?". Canadian Medical Association Journal. 185 (4): 309–316. doi:10.1503/cmaj.120951. ISSN 0820-3946.
- Media related to Grapefruit juice at Wikimedia Commons