Because it stimulates the "fight or flight" nervous system, high doses can lead to heart palpitations, anxiety, and restlessness. Since caffeine has a half-life of about 5–6 hours, a cup of coffee at 4:00 PM could still be stimulating your brain at 10:00 PM, ruining sleep quality.

It improves reaction time, vigilance, and short-term memory.

The brain eventually adapts to regular caffeine use by creating more adenosine receptors. This means you Finding the Sweet Spot

However, caffeine doesn’t activate them—it simply blocks them. It’s like putting a piece of tape over a keyhole so the key (adenosine) can’t get in. By preventing the "sleepiness signal," caffeine keeps you feeling alert. Additionally, this blockage often triggers a secondary release of dopamine and norepinephrine, which explains the mood boost and "jittery" excitement. The Benefits of the Buzz