Caffeine functions as a central nervous system stimulant. When it hits your brain, the most noticeable effect is alertness.
For healthy adults, the FDA has cited 400 milligrams a day, or roughly four to five cups of coffee, as an amount that is generally not associated with dangerous negative effects.
Caffeinated coffee is not recommended for: People with arrhythmias (for example, irregular heartbeats) People who often feel anxious.
Caffeine is a stimulant that can increase blood flow, blood pressure, and stress on the kidneys.