Over at Educated Guesswork, in a response to a post on "Me-too drugs", a commenter wonders why Grapefruit juice inhibits the metabolization of non-sedating antihistamines.
I'm glad you asked that question.
Grapefruit inhibits the activity of the liver enzyme cytochrome P450-3A4, which metabolizes about half of the medicines in the modern pharmocopia. (One third of the rest is handled by P450-2D6). One look at the list of drugs using, inhibiting or potentiating P450 might lead you to conclude that every pair of drugs will strongly interact. Check out Flockhart's canonical P450 interation table.
Of the thousands of interesting interaction inferences that can be made from this table, note this one: eating charbroiled meats should help reduce a coffee buzz.