Doses of caffeine equivalent to the amount normally found in standard servings of tea, coffee and carbonated soft drinks appear to have no diuretic action.  However, acute ingestion of caffeine in large doses (at least 250–300 mg, equivalent to the amount found in 2–3 cups of coffee or 5–8 cups of tea) results in a short-term stimulation of urine output in individuals who have been deprived of caffeine for a period of days or weeks.  This increase is due to both a diuresis (increase in water excretion) and a natriuresis (increase in saline excretion); it is mediated via proximal tubular adenosine receptor blockade.  The acute increase in urinary output may increase the risk of dehydration . However, chronic users of caffeine develop a tolerance to this effect, and experience no increase in urinary output.