How does caffeine block adenosine

Caffeine blocks adenosine by competing for its receptors: it occupies them without activating them, so adenosine cannot deliver its usual sleepiness signal. 1

• Adenosine builds up while you’re awake and creates sleep drive; the longer you’re awake, the more sleepy you tend to feel. 2
• Caffeine occupies A1 and A2 receptors but does not clear the adenosine that has accumulated; it blocks adenosine from binding and signaling through those receptors. 3 4
• When caffeine wears off, adenosine can bind again, including the adenosine that built up while its effects were blocking the receptors, which can contribute to a caffeine crash and pronounced sleepiness. 5
• Caffeine masks fatigue rather than creating more energy: it shifts when sleepy signals are felt, while regular daily use can become something people rely on to feel normal rather than a lasting boost above baseline. 6 7