Caffeine acts primarily as a central nervous system stimulant. It also increases mental
alertness and helps one stay awake longer. Some studies have shown that consuming
caffeine provokes secondary effects in people who have certain sensitivities such as
insomnia, headache, irritability, and nervousness. Most notably, caffeine causes
difficulty falling asleep, inhibits deep sleep, and lowers the ability to wake easily. In
other words caffeine diminishes our fatigue perception threshold. Just one 100 mg dose
can postpone the onset of sleep particularly for those who don’t regularly consume
caffeine or who already suffer from insomnia.