Caffeine: Is it dehydrating or not? It is true. Researchers used to believe that caffeinated drinks had a diuretic effect. This means that you would urinate more after drinking them, which could increase your risk of becoming dehydrated. Recent research shows that this is not true and that caffeine only has a diuretic effect if you consume large amounts of it — more than 500 to 600 milligrams (or 4 to 7 cups of coffee) a day.
Still, caffeinated drinks can make you jittery, sleepless or anxious. Water is probably your best bet to stay hydrated. It's calorie-free, caffeine-free, inexpensive and readily available.
