Grapefruit juice has long been known as the juice to avoid when you or your kids are taking medicine (not that more than a drop has ever passed any child's pursed lips); it can increase the potency of certain drugs. But now it looks like kid-friendly apple and orange juice may also be risky mixes with meds: They appear to make some drugs less effective, and may even wipe out their potential benefits. "These juices block some medications from being transported into the bloodstream. It's like they miss the shuttle bus," says researcher David G. Bailey, a professor of clinical pharmacology at the University of Western Ontario. Bailey specifically looked at a common over-the-counter antihistamine, but he says there's evidence these drinks can impact other drugs as well. Until more research is complete, play it safe: "Take drugs with water and wait three to four hours before offering juice," he says. "That's a good way to make sure that the drug will be adequately absorbed."