Caffeine may be found in its natural state in many plants, including tea leaves, coffee beans, and cocoa nuts. The pure form of caffeine is a bitter, white, crystalline powder derived from the decaffeinating process of coffee and tea. The vast number of products in which caffeine comes, range from coffee, to tea, to colas, to milk chocolate, and to pain relievers, just to mention a few.

Most people are unaware of caffeine's addictive properties. Those who consume 300 mg. or more per day, suffer from withdrawal symptoms if they abruptly cut off their caffeine supply. Most users will suffer from symptoms of fatigue and depression, irritability, tremors, jumpiness, deprivation of deep sleep, and vascular headaches, as the blood vessels in the brain dilate. Caffeine, however, can be medically useful as a cardiac stimulant, and also as a mild diuretic used to flush the system.

One of the mechanisms that caffeine addiction and cocaine addiction share, is that they block an adenosine's ability to slow the nerve cells' activity in preparation for sleep, and instead increase the speed of their activity and of the neuron firing in the brain. The caffeine causes the blood vessels in the brain to constrict, because it has blocked the adenosine's ability to open them to allow sleep. The ability of caffeine to close the blood vessels is why many pain relievers contain caffeine. If a person has a vascular headache, the caffeine in the medicine will shut down the blood vessels, thus easing the pain.

The increased neuron firing in the brain triggers the pituitary glands to release hormones that tell the adrenal glands to produce adrenaline, also known as epinephrine. Adrenaline, the "fight-or-flight" hormone, gives the user's body a boost, and heightens the person's alertness.

One final mechanism caffeine and cocaine share, is their ability to manipulate dopamine production. Dopamine, a neurotransmitter, activates the "pleasure centers" in certain parts of the brain, and simply makes a person feel good. Naturally, the pleasurable effect produced by dopamine manipulation plays a prominent role in caffeine addiction.

The short-term effects resulting from caffeine consumption, such as alertness, renewed energy, and pleasure, may not necessarily outweigh the longer-term effects of caffeine addiction. Caffeine, despite its similarities to amphetamines, has side effects that are not nearly as severe, and withdrawal symptoms that are, generally, not life-threatening.

---source