How does caffeine affect your sleep and energy levels?

Caffeine works by blocking adenosine receptors in the brain. Adenosine is a chemical that builds up throughout the day and makes you feel sleepy, so when caffeine blocks it, you feel more alert and awake. The energy boost is essentially borrowed, though, because the adenosine keeps accumulating behind the scenes. The sleep impact is significant because caffeine has a half-life of about 5 to 7 hours, meaning half of a 3pm coffee is still in your system at 9pm. This delays sleep onset, reduces deep slow-wave sleep, and shortens overall sleep duration even if you fall asleep normally. Poor sleep then increases fatigue the next day, which drives more caffeine consumption, creating a cycle of dependency and diminishing returns over time.