Why stop at grapefruit juice? I've heard citrus juice can have unpredictable effects on any drug.

Imagine you have a peanut allergy and have to check the labels on everything to see if it contains peanut or processed in a plant with peanuts.

Then you walk into the drinks aisle and see grapefruit juice box with a big red banner WARNING THIS PRODUCT CONTAINS GRAPEFRUIT JUICE.