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.