Many people try to compensate for a lack of sleep or energy with a few extra cups of coffee during the day. Unfortunately, caffeine is not the ideal remedy for fatigue. After just three short nights of about five hours of sleep, the effect of caffeine is already reduced. Caffeine won’t keep you sharp or “awake” if you’ve had several nights of poor sleep.
A study commissioned by the U.S. Department of Defense investigated the effect of caffeine after periods of short sleep. After three nights of disturbed sleep, 24 participants who took 200 mg of caffeine twice a day did not perform better on psychological tests than the 24 participants who received a placebo. So caffeine is not an effective stimulant for sleep-deprived brains.
In addition, drinking coffee in the evening or late afternoon can disrupt your sleep at night.