Caffeine dependence


is a commonplace central nervous system stimulant drug which occurs in nature as part of the coffee, tea, yerba mate, cocoa and other plants. It is also an additive in many consumer products, most notably beverages advertised as energy drinks and colas.
Caffeine's mechanism of action is somewhat different from that of cocaine and the substituted amphetamines; caffeine blocks adenosine receptors A1 and A2A. Adenosine is a by-product of cellular activity, and stimulation of adenosine receptors produces feelings of tiredness and the need to sleep. Caffeine's ability to block these receptors means the levels of the body's natural stimulants, dopamine and norepinephrine, continue at higher levels.
The Diagnostic and Statistical Manual of Mental Disorders describes four caffeine-related disorders including intoxication, withdrawal, anxiety, and sleep.

Dependence

Mild physical dependence can result from long-term caffeine use. Caffeine addiction, or a pathological and compulsive form of use, has not been documented in humans.
Studies have demonstrated that people who take in a minimum of 100mg of caffeine per day can acquire a physical dependence that would trigger withdrawal symptoms that include headaches, muscle pain and stiffness, lethargy, nausea, vomiting, depressed mood, and marked irritability. Professor Roland R. Griffiths, a professor of neurology at Johns Hopkins in Baltimore strongly believes that caffeine withdrawal should be classified as a psychological disorder. His research suggested that withdrawal affects 50% of habitual coffee drinkers, beginning within 12–24 hours after cessation of caffeine intake, and peaking in 20–48 hours, lasting as long as 9 days.
Continued exposure to caffeine leads the body to create more adenosine receptors in the central nervous system which makes it more sensitive to the effects of adenosine in two ways: it reduces the stimulatory effects of caffeine by increasing tolerance, and it increases the withdrawal symptoms of caffeine as the body becomes more sensitive to the effects of adenosine once caffeine intake stops. Caffeine tolerance develops very quickly. Tolerance to the sleep disruption effects of caffeine were seen after consumption of 400mg of caffeine 3times a day for 7days, whereas complete tolerance was observed after consumption of 300mg taken 3times a day for 18days.