Calories in Grapefruit juice, red, not fortified, not from concentrate

What makes grapefruit juice so powerful?

In 1989, researchers at a Canadian hospital were studying how the blood-pressure drug felodipine interacted with alcohol. To mask the alcohol's taste, they used grapefruit juice as a mixer — and noticed something unexpected: felodipine blood levels were far higher than anticipated, regardless of alcohol. The culprit turned out to be furanocoumarins, compounds naturally present in grapefruit that irreversibly inhibit CYP3A4, an enzyme lining the intestinal wall that normally breaks down a wide range of medications before they reach the bloodstream. With CYP3A4 disabled, drugs like certain statins, calcium channel blockers, and immunosuppressants can enter circulation at multiples of their intended dose, sometimes dangerously. The effect persists until the intestinal lining regenerates — roughly 72 hours after a single glass. Red grapefruit juice also contains lycopene, the same carotenoid pigment responsible for the red color of tomatoes, which is unusual among citrus. Unlike white grapefruit varieties, red cultivars like Ruby Red accumulate lycopene in their juice sacs, giving the pressed juice its distinctive pink-red hue without any added coloring.