Caffeine can make some people feel tired despite its reputation as a stimulant. This happens because caffeine blocks adenosine receptors in the brain—a chemical responsible for making you feel sleepy. When caffeine wears off after being metabolized, there is a rebound effect where adenosine can bind to its receptors again, causing increased sleepiness. Additionally, regular caffeine consumption can build tolerance, requiring more caffeine to achieve the same stimulating effects; without sufficient caffeine, tiredness may increase. A sudden drop in caffeine's effects can lead to a "caffeine crash," characterized by headaches, tiredness, irritability, and difficulty concentrating. Therefore, caffeine can indeed make you tired, especially after its initial stimulating effects wear off or with excessive or regular use.