Some people theorize grapefruit juice can extend your coffee's caffeine effects by slowing metabolism, but a chemistry professor says results aren't guaranteed.
https://www.foxnews.com/food-drink/grapefruit-could-make-coffee-buzz-last-longer-experts-warn-hidden-risks
https://www.foxnews.com/food-drink/grapefruit-could-make-coffee-buzz-last-longer-experts-warn-hidden-risks