List of drugs affected by grapefruit

Grapefruit and grapefruit juice have been found to interact with numerous drugs, in many cases resulting in adverse effects. Some other citrus fruits can have similar effects; one medical review advised patients to avoid all citrus.

The furanocoumarins (and to a lesser extent the flavonoids) are responsible for the effects. These active materials inhibit a key enzyme ( isoform CYP3A4) which is responsible (among other activities) to drug metabolism. The effect happens in two ways. One is that grapefruit can block the hepatic CYP3A4 thereby affecting the medication metabolism. If the drug is not metabolized, then the level of the drug in the blood can become too high, leading to an adverse effect. On the other hand, if the medication is provided as a pro-drug, compromising its metabolism may prevent the drug from being created, thereby reducing its therapeutic effect. The other effect is that grapefruit can block the enterocyte CYP3A4 thereby affecting the medication absorption in the intestine. If the medication is absorbed to a lesser extent, it may not reach a therapeutic level and its effect may be compromised.

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.

Grapefruit contains a number of polyphenolic compounds, including the flavanone naringin, alongside the two furanocoumarins, bergamottin and dihydroxybergamottin. Organic compounds that are furanocoumarin derivatives interfere with the hepatic and intestinal enzyme isoform CYP3A4 and are believed to be primarily responsible for the effects of grapefruit on the enzyme. Bioactive compounds in grapefruit juice may also interfere with P-glycoprotein and organic anion transporting polypeptides (OATPs), either increasing or decreasing the bioavailability of a number of drugs.

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