In 1989, a group of Canadian researchers studying a blood pressure drug were astonished to discover that drinking a glass of grapefruit juice dangerously increased the drug's potency.

They were testing the effects of drinking alcohol on a medicine called Plendil. The scientists needed something that would hide the taste of alcohol so that subjects would know only that they were taking the drug and not know whether they were drinking alcohol with it.

"One Saturday night, my wife and I tested everything in the refrigerator," said David G. Bailey, a research scientist at the London Health Sciences Center in London, Ontario, and the lead author on the study. "The only thing that covered the taste was grapefruit juice."

So they used it in their experiment, expecting the grapefruit juice to be irrelevant to their results. But blood levels of the drug went up significantly in the control group that drank just grapefruit juice, without alcohol.