atropine (ătˈrəpēn, –pĭn) [key], alkaloid drug derived from belladonna and other plants of the family Solanaceae (nightshade family). Available either as the tincture or extract of belladonna, or as the pure substance atropine sulfate, it is a depressant of the parasympathetic nervous system. It has some chemical similarity to the body substance acetylcholine and interferes with nerve impulses transmitted by that substance. Atropine produces rapid heart rate, dilated pupils, dry skin, and anesthetizes the nerve endings in the skin. Because it relaxes smooth muscle and suppresses gland and mucous secretions, it has been used to treat peptic ulcer by reducing the production of stomach acid. Atropine is given before general anesthesia to keep the air passages clear and is an ingredient in various preparations for symptomatic relief of colds and asthma. It also acts as an antidote in poisoning from such agents as mushrooms, morphine, prussic acid, and nerve gas, but overdosage causes delirium, convulsions, and coma. A related alkaloid, scopolamine, is used mainly as a sedative.