A 2012 clinical trial at the University of Chicago showed that having a glass of grapefruit juice daily while taking the anticancer drug sirolimus provides three times the drug’s benefit, since the juice slows metabolism of the drug. This means patients may be able to take lower doses of that drug, reducing side effects and costs (dosage is still being studied). Please note: Grapefruit and some other citrus fruit interact negatively with a number of drugs; if you love them, check with your doctor or pharmacist before having them with your meds.