Caffeine has a half-life of three to five hours in a person's system, so it remains in the body for eight to 14 hours, according to the American Academy of Sleep Medicine. The effects of caffeine in the blood system peak 30 to 60 minutes after intake.
The effects of caffeine wear off more quickly for regular drinkers because they develop a tolerance for it, reports the AASM. Coffee and tea are the most dominant sources of caffeine intake for Americans. Consumption in the United States averages 200 milligrams per day, which is three times the world average. Moderate intake can improve a person's alertness, reaction time and mood.