As I have said Caffeine stimulates the central nervous system and can produce different symptoms through out the rest of the body. Some times people experience a caffeine overdose (”caffeinism”).The effects varies according to individual body size and type and the amount of caffeine consumed. Doses ranging from 250 to 750 mg ,which is 2 to 7 cups of coffee, this can produce restlessness, nausea, headache, sleep disturbances, and irregular heart beats. In some cases it may also causes an eating disorder called anorexia. Doses of over 750 mg ,seven cups of coffee, can produce a reaction similar to an anxiety attack: the symptoms include being delirious, ringing ears, and light flashes.