This delays the onset of drowsiness and releases dopamine.Studies have demonstrated that people who take in a minimum of 100 mg of caffeine per day (about the amount in one cup of coffee) 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. 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 decreases. Caffeine tolerance develops very quickly. Tolerance to the sleep disruption effects of caffeine were seen after consumption of 400 mg of caffeine 3 times a day for 7 days, whereas complete tolerance was observed after consumption of 300 mg taken 3 times a day for 18 days. Physiological effects
When a person becomes caffeine dependent, it can cause a person to suffer different physiological effects which could lead to withdrawal.
Children and Teenagers
It is not recommended for children under the age of 18 to consume several caffeinated drinks according to the American Academy of Pediatrics (AAP). If they were to consume caffeine it is recommended to follow some guidelines so they do not consume too much throughout the day. If they do, they can become dependent on caffeine and without it can suffer many different side effects. These include increase of heart rate and blood pressure, sleep disturbance, mood swings, and acidic problems. Long lasting problems on childrens nervous system and cardiovascular system are currently unknown and studies are still being conducted on it. Tolerance
Tolerance levels regarding caffeine typically vary from person to person. Caffeine tolerance occurs when the stimulatory effects of caffeine decrease over time due to regular consumption. According to H.P. Ammon from the National Library of Medicine, caffeine tolerance occurs when the body responds to an intake of caffeine through the up-regulation of adenosine-receptors. References


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