Regular caffeine use can trigger a physical dependence, a mild form of addiction. Caffeine has several physiological effects on the body. Medically, caffeine is useful as a cardiac stimulant and also as a mild diuretic (it increases urine production). It causes stimulation of the central nervous system. This manifests as greater wakefulness. On the vascular system, caffeine has two opposite impacts: vasodilatation (peripheral effect) and vasoconstriction (central effect). The final result is dependent upon the stronger of the effect and can cause hypotension, hypertension or nothing at all. Caffeine also causes greater secretion of stomach acid and can be unpleasant in people suffering from gastritis or peptic ulcers.