Coffee consumption can cause tiredness because the drink contains caffeine, which blocks the brain’s adenosine receptors- a chemical that increases when waking up and reduces during bedtime. While adenosine molecules are expected to attach to special brain receptors and reduce brain activity to promote sleep, caffeine limits this process. However, it does not prevent production of new adenosine molecules, and after some time, say 45 minutes, the caffeine fades in the body, leading to normal working of adenosine that causes sleepiness or fatigue. Again, regular coffee consumers can nurture caffeine tolerance. Excessive and frequent blocking of adenosine receptors can increase release of adenosine receptors to counter the high levels of caffeine consumed, thus increasing the chance of sleepiness.
