Quick Answer Why does coffee make me sleepy comes down to one molecule: caffeine blocks adenosine receptors without removing adenosine, so the sleep chemical keeps piling up behind the blockade and signals all at once when caffeine fades. A July 2026 review in Frontiers in Physiology confirms that caffeine's main action at normal doses is…
Quick Answer Caffeine is near fully absorbed within about 45 minutes of swallowing it, with blood levels peaking anywhere from 15 to 120 minutes depending on the person and what else is in their stomach. It gives you nothing. Caffeine works by blocking adenosine, the molecule that builds up in your brain while you are…
Quick Answer Caffeine has an average half-life of about 5 hours in healthy adults, so roughly half your dose is still circulating 5 hours after the last sip, and a quarter of it is still there at 10 hours. Full clearance usually takes somewhere between 15 and 30 hours depending on your liver enzymes, pregnancy…
