How long does it take to metabolize caffeine?
Caffeine has a half-life of about 5 hours.
Someone who consumes 40 milligrams (mg) of caffeine will have 20 mg remaining in their system after 5 hours.
When do effects peak?
Levels of caffeine peak in the blood within about 15–45 minutes of consumption.
They are then quickly metabolized by the liver.
Most people notice the strongest effects during this time, and many report feeling jittery, needing to urinate, and having sudden bursts of energy. These symptoms tend to go away as the caffeine starts to break down.