An alkaloid, C17H23NO3, with the chemical structure below. The sys­tematic chemical name is endo-(±)-a-(hydroxymethyl) phenylacetic acid 8-methyl- 8-azabicyclo[3.2.l]oct-3-yl ester, and in phamacy it is sometimes known as dl­hyoscyamine. It occurs in minute amounts in the leaves of Atropa belladonna, A. betica, Datura stramonium, D. innoxia, and D. sanguinea, as well as many related plants. It is chiefly manufactured by racemization of 1-hyoscyamine, which is isolated from the leaves and stems of the henbane, Hyoscyamus niger. It melts at 114-116°C (237-241 °F) and is poorly soluble in water. The nitrate and sulfate are used in medicine instead of the free base.
Atropine is used clinically as a mydriatic (pupil dilator). Dilation is produced by paralyzing the iris and ciliary muscles. Atropine is also administered in small doses before general anesthesia to lessen oral and air-passage secretions. Its ability to reduce these secretions is also utilized in several preparations commonly used for symptomatic relief of colds.