Fruits and vegetables are loaded with beneficial vitamins, minerals, flavonoids and phytochemicals. Citrus, including grapefruit, provides vitamin C and fiber, important for health. Even the DASH diet, a diet found to improve blood pressure, encourages the consumption of grapefruit. However, blood pressure medications may carry warning labels for this otherwise healthful fruit.
Grapefruit juice decreases the expression of the enzyme cytochrome P450 3A4 in the small intestine wall. This enzyme normally interferes with the availability of certain medications, including those taken for high blood pressure. By decreasing this enzyme, grapefruit juice allows more of the drug to be absorbed in the blood and increases its effect. This increased availability can lead to a dangerous drop in blood pressure.
Food and drug interactions may be avoided by ingesting them separately, as noted on medication warning labels. This does not hold true for grapefruit or its juice and blood pressure medication. The grapefruit juice effect duration may be up to 24 hours. There is no safe time to consume grapefruit juice when taking blood pressure medication.