Trigger checker for grapefruit juice

Serving size, prep, and portion notes for grapefruit juice

The most important thing about grapefruit juice is not a food sensitivity at all. Grapefruit contains furanocoumarins, bergamottin chief among them, which switch off CYP3A4, an enzyme lining the small intestine that normally breaks down a large share of an oral medicine before it ever reaches the bloodstream. Disable that enzyme and more of the dose gets through than the prescriber assumed, so blood levels of the affected drug rise. The inhibition is irreversible, meaning the gut has to build fresh enzyme, which takes on the order of a day or more, so drinking the juice at breakfast and taking the tablet at night does not get around it. The effect is drug specific rather than general: it matters a great deal for some statins, some calcium channel blockers used for blood pressure and some transplant immunosuppressants, and not at all for many other medicines, including some in those same families. That is precisely why the answer lives in your medicine leaflet or with a pharmacist rather than in a rule of thumb. On the food chemistry side grapefruit juice is milder than its reputation. It grades clean on histamine and, unlike whole grapefruit, clean as a histamine liberator, plus clean on gluten, caffeine, sulfites, nickel and dairy protein. Its own flags are moderate excess fructose, moderate salicylates and moderate for low-fermentation protocols.