Caffeine. Computer graphic of a molecule of caff- eine, an alkaloid drug found in coffee & tea, and which can be used to treat migraines and asthma. The molecule's atoms are represented by colour- coded cylinders: carbon (C) is grey, nitrogen (N) is dark blue, oxygen (O) is red and hydrogen (H) is turquoise. Caffeine has the chemical formula C8H10O2N4. The drug raises blood pressure, stimu- lates the central nervous system, promotes urine formation, and stimulates the action of the heart and lungs. Caffeine is used in treating migraine because it constricts the dilated blood vessels that can cause the condition. It relieves asthma attacks by widening the bronchial airways.