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How does caffeine work?

Medicine & HealthLesson on requestFree to read

Quick answer

Caffeine works by blocking the brain chemical that makes you feel sleepy. A molecule called adenosine builds up as you stay awake and slots into receptors to signal tiredness; caffeine fits those same receptors and jams the signal, so you feel alert.

Step by step

  1. Adenosine builds up and makes you feel sleepy.
  2. Caffeine blocks adenosine's receptors.
  3. With the 'tired' signal jammed, you feel alert.
  4. Effects fade as the body clears the caffeine.

People also ask

How does caffeine keep you awake?
It blocks adenosine, the chemical that signals tiredness, so your brain doesn't get the 'slow down' message.
Why does caffeine stop working for some people?
With regular use the brain makes more adenosine receptors, so you need more caffeine for the same effect — that's tolerance.
How long does caffeine last?
Roughly 4–6 hours for half of it to clear, which is why an evening coffee can disrupt sleep.