How does caffeine reach the brain after someone drink a coffee or tea?

After consuming coffee or tea, caffeine is absorbed into the bloodstream through the stomach and small intestine. It then circulates throughout the body, crossing the blood-brain barrier due to its ability to dissolve in lipids. Once in the brain, caffeine blocks adenosine receptors, which leads to increased alertness and reduced feelings of fatigue. The effects can typically be felt within 15 to 45 minutes after consumption.