To be clear, Breus is completely on board with how caffeine can hinder sleep. “Caffeine is arguably one of the biggest offenders in our sleep,” he says. The thing is, there’s a difference between regular, restorative sleep and a quick, 30-minute-long cat nap. For the latter, caffeine may be more friend than foe. 

“It turns out that a buildup of something called adenosine in your brain is what makes you feel sleepy,” notes Breus, as the compound slows down nerve cell activity in your brain (which causes drowsiness). What caffeine does is binds to those adenosine receptors and effectively speeds the nerve cell activity back up, which provides a jolt of energy. But here’s the thing: To your nerve cells, caffeine and adenosine look the same. “If you look at the molecular structure of adenosine and the molecular structure of caffeine, they’re off by one molecule,” notes Breus (here’s a diagram, the structural similarities highlighted in red). “The thing that makes us wake up and the thing that makes us go to sleep is literally off by one molecule.” 

So how does this relate to your midday nap? Well, says Breus, caffeine can actually fool your nerve cells for a time, as “those receptor sites will accept caffeine,” and allow you to sleep before the stimulant actually kicks in. It won’t last long (about 25 minutes before your sleep burns through the adenosine, he notes) but he says it can work for a little cat nap.  

https://www.mindbodygreen.com/articles/why-this-sleep-doctor-wants-you-to-take-a-caffeine-induced-nap