A pounding headache is the most common, and other symptoms include headache, sleepiness, lack of concentration, depression, irritability, nausea, psychomotor impairment, blurring of vision and a desire for caffeine. These symptoms are proportionate to caffeine's maintenance dose, sometimes lasting up to a week. Such addiction can also occur in people whose caffeine-intake is low. Christina Yeung, a nutritionist with Nature's Farm gives a guide. It depends on the individual.
Some people have a higher tolerance for caffeine.
Though scientists can't seem to agree on whether caffeine can directly cause any health problems, there are several conditions have been consistently linked to caffeine consumption. For example, it can stimulate the production of gastric acid, leading to heartburn. It also increases calcium excretion, thus contributing to osteoporosis. However, two tablespoons of milk added to the coffee help offset this effect. Caffeine is also a diuretic - it increases the loss of water.