Many of your medications may have warnings of TAKE WITH FOOD or DO NOT EAT 30 MINUTES BEFORE OR AFTER THIS MEDICATION because oral drugs may upset the stomach or not be absorbed as well depending on food intake. Some foods, like the grapefruit, can act like a drug themselves.
Grapefruit juice contains a chemical called bergamottin (and 6’,7’-dihydroxybergamottin, which were first found in bergamot oranges). This chemical is a specific inhibitor of an enzyme in your liver and small intestine called cytochrome P450, family 3, subfamily A, polypeptide 4 (CYP3A4) that usually metabolizes macromolecules (lipids, proteins), but also drugs and toxins. Depending on the drug, CYP enzymes can either increase or decrease the amount of active drug in your circulation (called bioavailability). There are warnings not to drink grapefruit juice with some statin medications because that would increase the bioavailability of the statin and could cause side effects and organ damage.
Some researchers are actually using the power of the grapefruit to benefit patients. They are investigating whether grapefruit juice could be used as a ‘drug booster’ – the drug dosage could be lowered, but the resulting bioavailability would be the same. Using less drug would translate to a lower cost to the consumer. During Phase I trials in humans, researchers determined that an 8-oz. daily glass of grapefruit juice increased the bioavailability of 25 mg of sirolimus (a possible anti-cancer drug that is currently used as an immunosuppressant) to that of 90 mg of sirolimus alone. That translates into taking 25% of the usual drug dose but seeing the same effects of the drug on cancer cells.
There are a couple of drawbacks to using grapefruit as a prescription. The concentration of bergamottin can vary between grapefruit juice batches. The authors of the Phase I study contacted the Florida Department of Citrus to obtain a frozen concentrate that was tested for bergamottin levels before they used it. The other inconsistency is the variation between individuals. Some people have higher levels of CYP3A4 enzyme in their small intestine (as much as 40-fold), and those people see the greatest effect from grapefruit juice.
Grapefruit could be a powerful medical tool because it is a natural, easily available, low-cost food that has a specific and well-known molecular mechanism. Who said money doesn’t grow on trees?