But it turns out that the caffeine in your coffee is incredibly similar to adenosine in structure. The caffeine works it’s way through your bloodstream and into your brain, where it starts to compete and bind with adenosine receptors. But because it’s not adenosine, the sleepiness effect isn’t felt. Adenosine can no longer bind, meaning it’s calming properties are diminished. Which is great for you when you’re feeling tired. However, with long term use of caffeine your brain responds by creating more adenosine receptors, which means more caffeine is required to elicit the same response. It also means that when you try to quit drinking coffee or miss you daily intake, you might experience some withdrawal symptoms and feel more tired than you would have before you ever drank coffee.