Why does coffee make you go to the bathroom?

It works like a wter pill diuretic,that is why you pee. Coffee also produces a laxative effect in susceptible people through stimulation of rectosigmoid motor activity, as soon as four minutes after drinking. Even modest doses of coffee can have this effect, whether or not the body is ready to dispose of the feces, resulting in loose stools. Studies show that decaffeinated coffee has a similar stimulant effect on the GI tract proving that the laxative effect is not only due to caffeine. although caffeine (found in coffee) is often said to be a diuretic, this is not strictly true. It is likely that the apparent diuretic effect is actually caused by increased blood pressure (another effect of caffeine)