Causes drowsiness
Sorry this answer is incorrect. Caffeine actually increases the heartbeat, respiration, basal metabolic rate, and the production of stomach acid and urine and it relaxes smooth muscles, notably the bronchial muscle. Caffeine is absorbed through the stomach and small intestine into the bloodstream. The amount of caffeine in the blood reaching the brain determines the severity of its effects on the body. It is metabolized by the liver and eventually its metabolites are excreted in the urine.