Grapefruit and its juice (fresh or frozen) can either increase or, less frequently, decrease the effects of some drugs. Grapefruit contains substances that can interfere with the transformation and elimination of certain drugs resulting in serious adverse reactions.
As little as 200 mL (less than a cup) of juice or a whole grapefruit can cause a significant increase of blood levels of certain drugs. The effects of grapefruit can last up to 3 days, sometimes even longer. Because the effects of grapefruit last a long time, they cannot be avoided by spacing medication and grapefruit apart. Drinking grapefruit juice in the morning, for example, and then taking your medication at night will not eliminate the risk of interaction.
Grapefruit interactions are highly unpredictable. Not everyone will react the same way; it depends on which drug is involved, the grapefruit itself, and how sensitive you are to these effects.
To minimize the risk of drug interaction, refrain from eating grapefruits or drinking grapefruit juice before checking with your pharmacist. Other citrus fruits may produce similar effects to grapefruit, including:
- Seville oranges (used in marmalade)
Other citrus fruits (e.g., lemon, Navel or Valencia sweet orange, tangerine and clementine) do not cause this interaction.
Consumption of other fruits or their juices combined with other medications should also be avoided, such as:
- Carambola (starfruit)
Be alert and avoid taking your medications with grapefruit before checking with your pharmacist or physician.