an alkaloid found in henbane (hyoscyamus niger), and regarded as its active principle. it is also found with other alkaloids in the thorn apple and deadly nightshade. it is extracted as a white crystalline substance, with a sharp, offensive taste. hyoscyamine is isomeric with atropine, is very poisonous, and is used as a medicine for neuralgia, like belladonna. called also hyoscyamia, duboisine, etc.