Caffeine makes you tired.

Here's the irony. The reason that people get hooked on drinking coffee, particularly in the morning, is because it makes them feel better, more energised and alert. But does coffee actually increase your energy and mental performance, or just relieve the symptoms of withdrawl? Coffee is addictive and drinking it relives the symptoms of withdrawl.
Not only is coffee addictive, but also it worsens mental performance. Moderate and high consumers of coffee were found to have higher levels of anxiety and depression than abstainers.
Caffeine blocks the receptors for a brain chemical called adenosine, whose function is to stop the release of the motivating neurotransmitters dopamine and adrenalin. With less adenosine activity, levels of dopamine and adrenalin increase, as does alertness and motivation. Peak concentration occurs 30 - 60 minutes after consumption.
The more caffeine you consume, the more your body and brain become insensitive to its own natural stimulants, dopamine and adrenalin. You then need more stimulants to feel normal, and keep pushing the body to produce more dopamine and adrenalin. The net result is adrenal exhaustion - an inability to produce these important chemicals of motivation and communication. Apathy, depression, exhaustion and an inability to cope set in.
Coffee isn't the only source of caffeine. There's as much in a cup of strong tea as in a cup of regular coffee. Caffeine is also the active ingredient in most cola and other energy drinks such as red bull. Chocolate and green tea also contain caffeine, but much less than these drinks.