Caffeine temporarily blocks adenosine receptors to increase alertness, leading to rebound sleepiness as it is metabolized.

“Yes, you'll offset fatigue. You'll offset sleepiness because that adenosine simply can't function. But at the point where the caffeine becomes dislodged from the adenosine receptors, you will have a massive glut, a backlog of adenosine, and you will feel extra, extra sleepy.”

“You're not really getting more energy. You're actually borrowing energy against an overall system that is frankly nonnegotiable. What do I mean by that? Well, let's say that you were to wake up after six or eight hours of sleep and to drink a lot of caffeine and keep drinking caffeine throughout the day blocking those adenosine receptors. Yes, you'll offset fatigue. You'll offset sleepiness because that adenosine simply can't function. But at the point where the caffeine becomes dislodged from the adenosine receptors, you will have a massive glut, a backlog of adenosine, and you will feel extra, extra sleepy.”

“because caffeine acts as an adenosine antagonist effectively while caffeine is present in those receptors you don't feel as sleepy you have more energy you're reaction time goes down memories enhance Focus performance of all kinds yes but then when that caffeine is dislodged from the receptor then the adenosine can act even more potently at those receptors”

“it effectively blocks adenosine receptors. Adenosine is a molecule that builds up in your brain and body more and more according to how long you've been awake. It makes you feel sleepy.”

“Caffeine blocks the adenosine receptor, and then when it is dislodged from that receptor, whatever adenosine has built up and is around can then bind to the adenosine receptor. It makes you feel very sleepy. That's the caffeine crash.”

“caffeine does have anti-fungal properties that's probably one of the reasons potentially one of the reasons that coffee plants produce caffeine as you'll see in the next section there is more mold that grows on decaffeinated coffee there are more mycotoxins into caffeinated coffee beans caffeine is toxic at high doses it does have a ld50 a lethal dose 50.”

“Caffeine as i said is a methylxanthine it's going to block a wide range of adenosine receptors and phosphodiesterase the mechanism isn't terribly important other than to say that adenosine signals sleepiness in humans and if you block that that's probably why we have a stimulant effect to caffeine in the human body”

“the way that caffeine works comes back to our discussion of adenosine which is that adenosine builds up it's a sleepiness signal it's telling your brain get to sleep get to sleep the longer the more that you have caffeine rushes into the brain and it latches on it hijacks those adenosine receptors and it just blocks them”