"Because it’s not just the half life, caffeine has a quarter life, meaning it’s still has its hooks in my patient long after that morning sip. According to sleep scientist Matthew Walker, author of Why We Sleep, caffeine’s quarter life is about double its half life. This means that slow metabolizers like my patient may still be feeling the effects of their morning coffee well into the night. No wonder caffeine has been shown to be so disruptive of sleep. 4 After all, it binds to and blocks our adenosine receptors, the signaling pathways the body uses to fall asleep each night."