According to the National Institutes of Health, caffeine is a mild diuretic, which means it makes the body process fluids faster. WebMD states that people who consume or drink caffeine are more likely to head to the bathroom as caffeine makes the body lose water faster by urinating more.
In addition, WebMD reports that drinks that contain caffeine, such as coffee, tea, soda and energy drinks, are not ideal for quenching thirst. It is important to drink more water when one is working out to ensure that the body doesn't get dehydrated. A study by the Cooperative Extension Service in Clemson University, however, indicated that while coffee has a diuretic effect, the water consumed together in a cup of coffee or tea balances the diuretic effect.