sympathomimetic drug (sĬmpăth´ōmĬmĕt´Ĭk), any of a group of substances whose actions resemble the response of stimulated sympathetic nerves (see nervous system). These drugs include epinephrine and other catecholamines that are naturally produced in the body, and chemically similar substances such as ephedrine. Sympathomimetic drugs excite the central nervous system and heart and affect the diameter of blood vessels. They are used as decongestants and to alleviate bronchial asthma. Because they inhibit the production of the body substance histamine, they are prescribed for allergic conditions along with antihistamines.