Great news! Caffeine was once thought to be a significant diuretic, but that’s actually not true. Unless it’s consumed in large quantities (more than 500 to 600 mg a day, or two coffees) there aren’t such negative effects. In fact, studies have shown that urine output isn’t significantly changed when a person drinks a caffeinated beverage, rather than something non-caffeinated like water. So, as long as you enjoy your coffee in moderation, there’s not much to worry about.