How Caffeine Keeps You Awake
Caffeine blocks adenosine, a brain chemical that builds up during wakefulness and promotes sleepiness. By temporarily reducing sleep pressure, it helps you feel alert and focused.
How Much Caffeine Is Effective
Most adults feel increased alertness with 50 to 200 mg of caffeine, roughly one to two cups of brewed coffee. Lower doses can work for sensitive people, while higher doses may not add much extra benefit and can cause side effects.
How Long Caffeine Lasts
Caffeine reaches peak blood levels within 30 to 60 minutes and has a half-life of about 3 to 5 hours, meaning half the caffeine remains in your system after that time. For many people, a moderate dose taken earlier in the day supports wakefulness without seriously disrupting nighttime sleep. The FDA offers general guidance on caffeine and safety.
