Does Grapefruit Juice Make a Coffee Buzz Last Longer? Probably not.

Food & Wine takes a look at evidence suggesting that pairing a cup of Joe with grapefruit may extend the effects of caffeine. Michelle Francl, a professor of chemistry at Bryn Mawr College, is skeptical. “Grapefruit juice doesn’t seem to be a strong inhibitor of CYP1A2, so how long it extends the buzz may not be all that long," she says. "And it turns out that people’s ability to metabolize caffeine is pretty variable; some people clear it quickly, but others not so much.”