Henbane plant (Hyoscyamus niger) and flowers, illustration. This poisonous plant contains the chemicals hyoscyamine and scopolamine (hyoscine). These are used medicinally to relieve pain in arthritic joints. Henbane has also been used as a sedative to treat nervous disorders. Scopolamine is used in modern medicine to prevent motion sickness. Overdoses of the plant or its preparations may be fatal.