Coffee works by delivering a concentrated dose of caffeine to the body. A standard cup typically contains around 90–100 mg of caffeine, which blocks adenosine — the neurotransmitter that signals tiredness.
Because the caffeine enters the bloodstream quickly, the effect is immediate. Within minutes, alertness increases.
However, that rapid spike can come with side effects.
Many coffee drinkers notice symptoms like:
• jittery energy
• increased heart rate
• nervousness or anxiety
• a noticeable crash later in the day
For some people, this leads to a cycle of drinking multiple cups throughout the day just to maintain energy.