How does caffeine make people feel more alert?
Caffeine makes people feel more alert mainly by blocking a chemical called adenosine in the brain. Adenosine gradually builds up while we are awake and binds to receptors that promote sleepiness and relaxation. Caffeine has a similar structure to adenosine, so it can occupy these receptors without producing the same sleepy effect.
As a result, the brain receives fewer signals telling it to slow down, which can temporarily reduce feelings of tiredness and increase alertness, attention, and wakefulness. Caffeine may also indirectly increase the activity of certain brain chemicals involved in alertness.
The effects usually begin within about 15–45 minutes after consuming caffeine and can last for several hours, although this varies from person to person. Regular caffeine consumption can also lead to tolerance, meaning its effects may become less noticeable over time.
