Medicine & Health
How does caffeine work?
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.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how caffeine works.
Step by step
- 1Adenosine builds up and makes you feel sleepy.
- 2Caffeine blocks adenosine's receptors.
- 3With the 'tired' signal jammed, you feel alert.
- 4Effects fade as the body clears the caffeine.
Frequently asked questions
- 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.