How long does caffeine's effect last?

Caffeine has a duration of action characterized by its half-life and quarter-life. According to Matthew Walker, caffeine typically has a half-life of 5 to 6 hours. This means that after 5 to 6 hours, about half of the caffeine you consumed is still circulating in your system. Furthermore, caffeine has a quarter-life of approximately 10 to 12 hours. This implies that if you drink a cup of coffee around 2 PM, roughly a quarter of that caffeine could still be affecting your brain at midnight 1 2.